EQUINE Flashcards

Question

7 year old male Clydesdale horse presents for exercise intolerance and noisy breathing. On your exam, you note mild inspiratory dyspnea with an audible whistling sound on inspiration. What is the most likely diagnosis? a. Laryngeal hemiplegia b. Sinusitis c. Asthma d. Intrathoracic large airway obstruction

Answer 1

a. Laryngeal hemiplegia ## Footnote In this condition, the recurrent laryngeal nerve is damaged. Interestingly, the left side is almost always the side that is affected. An actual cause is usually not found, although direct trauma and certain toxins can cause laryngeal hemiplegia. It is thought to be a hereditary disorder. An intrathoracic large airway obstruction and asthma would both cause more expiratory dyspnea. Sinusitis may cause nasal discharge but is not likely to cause the signs this horse is showing.

Answer 2

c. Diaphragm ## Footnote Contraction of the diaphragm pushes the abdominal contents back, increasing the length of the thoracic cavity, and pulls the ribs abaxially. The external intercostal muscles assist in pulling the ribs abaxially. This ends up producing subatmospheric intrathoracic pressures and allows inspiration to occur. Contraction of the internal intercostal muscles and the muscles of the abdominal wall decrease lung volume and compress the chest wall. The diaphragm is important in this process because diseases altering innervation or strength of the diaphragm (such as botulism or phrenic nerve damage) or diseases preventing expansion of the diaphragm into the abdomen (such as large colon torsion) are important causes of respiratory distress and potentially hypoxemia and death.

Answer 3

a. Surgery ## Footnote Surgery is required so that you may stabilize the cervical vertebrae and decompress the spinal cord. There are two forms of cervical vertebral stenotic myelopathy (aka wobbler syndrome). One form is called cervical vertebral instability. In this case, ventroflexion of the neck results in spinal cord compression. Most commonly affected sites are C3-4 and C4-5. The other form is known as cervical static stenosis. In this case, the compression is continuous regardless of the neck position. Clinical signs are usually in the form of a wide-based stance, conscious proprioceptive deficits, ataxia, paresis, and spasticity which is worse in the hindlimbs. Anti-inflammatories and stall rest may temporarily decrease clinical signs but are typically not a long-term therapy.

Answer 4

e. Disrupts motor innervation to the orbicularis oculi ## Footnote The auriculopalpebral nerve is a branch of the facial nerve and is therefore motor only. The auriculopalpebral block is useful in providing eyelid akinesis by blocking motor innervation primarily to the orbicularis oculi, thereby allowing manipulation of the eyelids without putting pressure on an already painful eye. This block is motor only and does not provide any desensitization. The supraorbital/frontal nerve block can be used to block a branch of the ophthalmic division of the trigeminal nerve, desensitizing the middle two-thirds of the upper eyelid and forehead skin. It may also provide some motor block of the levator palpebrae superioris due to a branch of the oculomotor nerve which runs adjacent.

Answer 5

b. Cranial VII and VIII (left side); fracture of the basisphenoid bone ## Footnote The correct answer is damage to cranial nerves VII (facial nerve) and VIII (vestibular nerve) on the left side caused by fracture of the basisphenoid bone. This is a common injury when a fractious young foal rears up and falls backward on the poll. The basisphenoid bone becomes injured resulting in injury to cranial nerves VII and VIII. Damage to the facial nerve results in the muzzle deviation (opposite direction of the side of injury, in this case deviated to the right), ptosis of the left eye and drooping of the left ear. Damage to the vestibular nerve results in the head tilt.

Answer 6

b. CN VI ## Footnote This nerve does not run along the guttural pouch in contrast to the others listed. Both the internal and external carotids may be affected during a guttural pouch infection. In case you don't remember, the guttural pouch in a horse is the air-filled diverticula of the auditory tube which communicates between the middle ear and the pharynx. Sometimes foreign material will get trapped there and result in infection.

Answer 7

d. 10-14 days ## Footnote Typically, the incubation period for tetanus is about 2 weeks, because it takes time for the spores to grow in an anaerobic environment before they produce toxin that can then be picked up by the nerves.

Answer 8

b. Ventricular septal defect (VSD) ## Footnote The image demonstrates a VSD or a hole in the intraventricular septum (identified by two markers). This is one of the more common congenital defects of the heart in horses. The murmur occurs as blood is shunted from the left side of the heart to the right during systole. Some horses can perform normally with a VSD while others, with large defects, can demonstrate heart failure. In this case, it was an incidental finding, as the horse was bright and alert at the time of exam. The remainder of the answers (ASD, PDA, and truncus arteriosus) can occur but are less common and would appear differently on echocardiography. It is unlikely but possible that you will be asked to interpret an echocardiogram on your board exam. If you are, this is likely to be one of the diseases you could be shown.

Answer 9

e. Quinidine ## Footnote Ideally, you would begin oral dosing of quinidine via a nasogastric tube at 2 hour intervals until there is conversion or toxicosis. An increase in the QRS duration of greater than 25% as compared to before initiation of treatment is considered a sign of toxicity. Clinical signs of toxicosis include colic, ataxia, hypotension, diarrhea, and edema. Digoxin will not convert an atrial fibrillation to a normal rhythm. However, it is indicated as adjunctive therapy when the vagolytic effect of quinidine causes a significant acceleration in ventricular response rate, the resting heart rate in excess of 90 beats per minute, if the horse is exhibiting a low vagal tone, or if conversion has not been achieved within 24 hours of initiating quinidine therapy. A precordial thump is ineffective, and defibrillation is only indicated during ventricular fibrillation, not atrial. Usually, there is an excellent prognosis for conversion if the horse has a heart rate of less than 60 beats per minute, atrial fibrillation of less than four months duration, and if there is a murmur less than or equal to a grade 3/6.

Answer 10

c. Hypotension ## Footnote Acepromazine will reliably cause hypotension. Acepromazine may cause paraphimosis in male horses, but this is not very common. However, because of this, many veterinarians will not use acepromazine on stallions. Acepromazine actually has anti-arrhythmogenic properties. Acepromazine does reduce the seizure threshold, but seizures are not as common as hypotension.

Answer 11

c. Strangulating lipoma ## Footnote Lipomas are a common cause of small intestinal obstruction in older horses. Typically, a section of the small intestine becomes intertwined with a pedunculated lipoma, resulting in obstruction and possible devitalization of the small intestine. Surgical correction is necessary to correct this problem. None of the other answer choices typically result in the clinical signs described, particularly gastric reflux. Left dorsal colon displacement typically have milder clinical signs, and the diagnosis can be made by rectal palpation and ultrasonography.

Answer 12

b. 65L ## Footnote To determine this answer you must figure out the deficit and calculate the horse's maintenance needs. The deficit is 35L (deficit x BW). Maintenance needs for a horse is approximately 60mL/kg/day. In this case, 30L. Adding the deficit and maintenance fluids together yields a total of 65 liters.

Answer 13

b. Neonatal Isoerythrolysis ## Footnote Neonatal Isoerythrolysis (NI) would be a possible cause of the icterus noted in the sclera. NI is common in multiparous mares and usually affects foals between 24-72 hours of age. NI results in hemolysis, hyperbilirubinemia, and icterus. A low packed cell volume would further support NI. NI develops because the newborn foal expresses alloantigens on its red blood cells inherited from the sire that the mare does not have. If the mare becomes sensitized to the sire's specific antigen, maternal antibodies are produced and absorbed by the foal soon after birth. This subsequently results in lysis of the red blood cells

Answer 14

c. Granulosa cell tumor ## Footnote Granulosa=theca cell tumors are the most comon ovarian tumor in horses and can cause increased levels of testosterone, sometimes causing aggressive behavior towards people. Another cause of aggression in horses is hypothyroidism.

Answer 15

c. Culicoides hypersensitivity ## Footnote Culicoides hypersensitivity is extremely pruritic and is also known as "sweet itch". Horses can be affected on their ventrum or dorsum, depending on the species of the fly. The horse develops a type 1 hypersensitivity to the flies' salivary antigens and develops excoriations, alopecia, and thickened skin as a result of scratching. The flies are more prevalent during the warmer seasons and are most active during dusk and dawn. Treatment includes controlling the fly population. Stabling the horses at dusk is often helpful because the flies rarely enter barns. Insecticides, stable blankets, and fans for circulating air in the stables may also be useful. The extreme pruritus and seasonality of the clinical signs is often enough to differentiate the Culicoides hypersensitivity from other skin diseases. Onchocerciasis is vectored by Culicoides, but is not seasonal and is not nearly as pruritic. Mosquitoes can be an annoyance and, more importantly, are vectors for more serious diseases such as the equine encephalitides. Tabanus flies and Chrysops flies cause pain to horses by lacerating them with their mouth parts to feed on their oozing blood. They do not cause pruritus and can be differentiated by their large, robust size.

Answer 16

d. Corynebacterium psuedotuberculosis ## Footnote Corynebacterium pseudotuberculosis is also known as pigeon fever. It causes an ulcerative lymphangitis and abscesses in the pectoral region of horses. Treatment is aimed at hot packing the swellings and draining the abscesses. Antibiotics can be administered but have been known to prolong the disease by delaying abscess formation. The other four answer choices classically present as crusting dermal lesions on horses.

Answer 17

a. Papiloomavirus is believed to play a role in the pathogenesis ## Footnote Sarcoids are one of the most common tumors in horses. They are considered non-metastatic tumors in virtually all cases. For this reason, small lesions are sometimes treated with benign neglect, but they are not expected to regress. More advanced lesions or tumors in certain sites do need to be treated more aggressively. Unfortunately, no single treatment is universally effective. Recurrence rates after surgical excision are approximately 50%. Although there is still controversy surrounding this issue, either bovine papillomavirus or an equine variant is thought by many to play a role in development of these tumors.

Answer 18

a. Anhidrosis ## Footnote Anhidrosis is the inability to sweat, which can be fatal if not addressed. The cause is unknown. It tends to occur in hot humid climates, and may occur in horses raised in the climate, or more commonly, horses brought into the climate. The most successful treatment is to move the horse back to a more favorable climate.

Answer 19

d. Hyperosmolality and decreased circulating blood volume ## Footnote In the horse, as in other species, ADH increases renal water reabsorption and urine osmolality by increasing permeability of the collecting tubules. Osmoreceptors in the hypothalamus detect subtle changes in plasma osmolality. If osmolality rises, you will hope to see ADH secretion so that the urine excreted would be more concentrated. The same is true if circulating volume decreases; thus, a lesser volume of water would be lost. When ADH secretion does not occur or if the kidneys are unable to respond to ADH, this is likely diabetes insipidus, and animals will be very polyuric, polydipsic and have extremely dilute urine.

Answer 20

a. Pergolide ## Footnote This case describes the typical presentation of equine pituitary pars intermedia dysfunction (PPID), sometimes referred to as equine Cushing's disease. The disease is a progressive disorder of pituitary pars intermedia enlargement (adenoma). The condition usually affects horses greater than 15 years of age and may affect any breed but ponies and Morgan horses have increased incidence. The classic symptom which is highly suggestive of this condition is hirsutism which is the symptom of a long curly hair coat that does not shed properly. Other symptoms include polyuria, polydipsia, laminitis, lethargy, excessive sweating or lactation, decreased muscle mass, infertility, and susceptibility to infections such as tooth root abscesses. Hirsutism as a clinical sign is the most sensitive indicator of PPID. Diagnosis of PPID by laboratory testing in horses with subtle signs can be challenging since no single test is absolutely sensitive and specific. Measurement of plasma ACTH concentrations is a simple and acceptable test, but must be compared to seasonal reference intervals as the concentration of ACTH fluctuates during the year (highest in the September, lower in January). Of practical note, the sample must be chilled or frozen until processing. Others have suggested the use of the thyrotropin-releasing hormone (TRH) stimulation test, which causes a significantly higher concentration of ACTH in PPID horses. However, TRH is may not be readily available. Finally, the dexamethasone suppression test has historically been used to diagnose PPID, but concerns in regard to steroid administration and the development of laminitis (or worsening of existing laminitis) has resulted in the test being used less frequently. Treatment aims to decrease clinical signs and does not typically result in a cure or complete remission of all signs. Pergolide is generally considered the treatment of choice. Pergolide is a dopamine agonist that is used to treat Parkinson's disease in humans. The drug acts to suppress pituitary hormone secretion. Older references will refer to the use of cyproheptadine which is a serotonin antagonist as a preferred treatment for PPID. There is also investigation that trilostane, a 3-beta hydroxysteroid dehydrogenase inhibitor may be useful in the management of PPID. Quinidine is used to treat atrial fibrillation in horses. Glargine is a long acting insulin analogue used in the treatment of diabetes mellitus. Levothyroxine is a synthetic thyroid hormone used to treat hypothyroidism. Dexamethasone is a corticosteroid and can be used to help establish a diagnosis of PPID but is not a treatment.

Answer 21

c. Diarrhea, fever, and neutropenia. Any 2 of the 3 diagnostic parameters qualify for isolation ## Footnote The most likely cause of the neutropenia is bacterial septicemia and endotoxemia due to gastrointestinal disease. Other common diseases that can cause a neutropenia are metritis and coliform mastitis.

Answer 22

c. Doudenitis-proximal jejunitis ## Footnote Duodenitis-proximal jejunitis, also known as either anterior enteritis, or proximal enteritis best fits this case because of the characteristic reflux, fever, peritoneal fluid characteristics, rectal findings, the depression and relatively less pain than would be expected with an obstruction. The cause is still uncertain, but a relationship of this disease to positive cultures of reflux for Clostridium difficile has been found. Typically these cases are treated medically, which would include repeated decompression of the stomach, IV fluids, replacement of electrolyte deficiencies, analgesics and correction of any acid-base abnormalities.

Answer 23

c. Psyllium ## Footnote Psyllium is a hemicellulose laxative that has the ability to bind with sand and help remove it from the gastrointestinal tract. Feeding the horse in a stall and/or utilizing hay racks will also help the inadvertent consumption of sand that may be ingested if a horse is eating on sandy ground. None of the other answer choices are as effective as psyllium.

Answer 24

c. Right dorsal colon displacement ## Footnote The rectal exam findings are characteristic for a right dorsal colon displacement. You can sort of figure out the answer even if you know nothing about horses, just think anatomy. The cecum is on the right side... so there is probably something going on in the right side. A left dorsal displacement is the same thing as a nephrosplenic entrapment. In this case, the colon becomes trapped in the renosplenic space. A primary cecal volvulus is rare in horses and are usually seen secondary to a large colon volvulus. These horses will ping similarly to a cow and usually present with acute colic. A strangulating lipoma is highly unlikely, given the age of the horse and lack of gastric reflux. Additionally, these tend to strangulate small intestines, not the colon.

Answer 25

c. Pseudomonas ## Footnote Pseudomonas is the most common agent causing bacterial keratitis in the horse. The gram negative cytology provides further evidence that it is the likely culprit. Staphylococcus can cause keratitis in horses but is gram positive. E. coli and Pasteurella are not agents that are commonly involved with keratitis in the horse.

Answer 26

a. Fescue ## Footnote Fescue ingestion leads to prolactin suppression and can result in thickened placenta, dystocia, or agalactia. Red maple causes Heinz body anemia. St John's wort causes photosensitization and hepatotoxicity. Pyrrolizidine alkaloids cause photosensitization and hepatotoxicity. Cantharidin causes colic.

Answer 27

b. Pyrrolizidine alkaloid ## Footnote The clinical signs described are typical for pyrrolizidine alkaloid toxicity. Consumption of this plant typically results in abnormalities in hepatic cell division; thus resulting in large hepatocytes known as megalocytosis.

Answer 28

a. Fetal or neonatal hemoabdomen ## Footnote The correct answer is fetal or neonatal hemoabdomen. All other choices listed were potential disease manifestations of MRLS. The exact pathogenesis of MRLS is still unknown, but the presence of eastern tent caterpillars was strongly associated with the disease. Later, experimental studies in which pregnant mares were exposed to or fed, via NG tube, eastern tent caterpillars resulted in early and late fetal loss.

Answer 29

d. Vesicular stomatitis ## Footnote VS affects horses, cattle and pigs with similar clinical signs. It is a viral disease of high morbidity and low mortality that appears about every 7 to 10 years in the Southwestern United States. Yearly outbreaks occur in southern Mexico and northern South America. Black flies and midges appear to be the vectors. Affected premises should be quarantined.

Answer 30

a. Foxglove ## Footnote This is a cardiotoxic plant

Answer 31

b. Prolonged gestation and decreased milk production ## Footnote Common clinical signs associated with fescue toxicosis include prolonged gestation and/or decreased milk production (agalactia). Ergopeptine alkaloids are ingested by the mare, which act as dopamine agonists. Dopamine serves to inhibit prolactin, thus inhibiting lactation. Placental thickening and weak or stillborn foals may also occur.

Answer 32

b. Streptococcus equi ssp. zooepidemicus ## Footnote This is a normal inhabitant of the guttural pouch. Streptococcus equi ssp. equi can be present when there is guttural pouch empyema. Aspergillus nidulans can be present in cases of guttural pouch mycosis. Salmonella should not be present in the guttural pouch.

Answer 33

c. \> 6 years of age ## Footnote RAO is a disease of mature horses older than 6 years of age. The direct cause is debatable but it has a progressive onset and is thought to be related to hypersensitivity to environmental factors. It is seen most commonly in the winter in stabled horses.

Answer 34

e. Equine Degenerative Myeloencephalopathy (EDM) ## Footnote The horse in this question has clinical signs most consistent with EDM; cervical vertebral malformation (wobblers) is also a possibility, but was not provided as an answer. The cause of EDM is unknown, but this disease typically affects young horses (\< 2-3 years of age; but older horses can develop disease). Clinical signs are a result of diffuse neuronal fiber degeneration of various portions of the central nervous system. This disease has been associated with low serum vitamin E concentrations, suggesting that oxidative damage may play a role in the development of disease. EMND is typically associated with muscle tremors, shifting of weight while standing, muscle atrophy and recumbency. Botulism is associated with generalized muscle weakness. Cauda equina syndrome causes analgesia of the perineum. EPM can cause a range of clinical signs, but is typically with asymmetric neurologic deficits.

Answer 35

b. A scotch tape test to confirm Oxyuris equi ## Footnote While all of these diagnostic tests are important when you suspect parasitism, the scotch tape test will enable you to observe the eggs stuck to the hair. The egg laying activity by the female worm is what causes the intense pruritis. Occasionally, eggs can be found in a flotation, which may give you a false negative interpretation if not found. A superficial skin scrape is a great alternative for this case; however, Chorioptes spp. tend to infest breeds with feathered legs. An infestation of Strongyloides vulgaris or Cyathostomes will likely cause colic, diarrhea, and lethargy.

Answer 36

d. Achilles tendon ## Footnote A complete laceration of the Achilles tendon involves rupture of the gastrocnemius and superficial flexor tendons. A gastrocnemius rupture alone may cause a dropped hock, but horses with this injury will still bear weight on the affected limb. Prognosis for this injury is grave.

Answer 37

d. Desmotomy of the accessory ligament of the deep digital flex ## Footnote This case describes a severe flexural deformity of the distal interphalangeal joint, also known as "clubfoot". This is typically a congenital condition in young horses although it can be acquired. A genetic component is suspected. Mild cases can sometimes be managed conservatively with NSAIDs, farriery, exercise and nutritional changes. Severe cases often require surgery; the surgical procedure of choice is desmotomy of the accessory ligament of the deep digital flexor tendon (also known as inferior check ligament desmotomy). The accessory ligament of the deep digital flexor tendon (inferior check ligament) runs from the palmar surface of the proximal metacarpus to the deep flexor tendon in the mid-metacarpal region. The superior check ligament originates above the knee and attaches to the superficial flexor tendon, and its primary purpose is to support the tendon. Superior check ligament surgery is used to treat a bowed tendon. Lateral digital extensor tenectomy is a procedure used to treat stringhalt. Transection of the insertion of the semitendinosus is used to treat fibrotic myopathy.

Answer 38

c. Nephrosplenic entrapment ## Footnote The kidney is obscured as a result of a left dorsal displacement of the large colon over the nephrosplenic ligament. Additionally, the spleen is pushed away from the body wall, making it difficult to see on ultrasound. Large horses may be predisposed to this. Besides surgical correction, one may try to roll the horse 360 degrees. Pain associated with these types of displacements are usually mild to moderate.

Answer 39

c. Lymphosarcoma ## Footnote Squamous cell carcinoma is the most common tumor of the equine stomach. Lipomas are seen commonly, but these do not involve the intestinal tract directly. Leiomyosarcomas are simply not as common as lymphosarcoma. Unfortunately, the prognosis in horses with lymphosarcoma is extremely poor.

Answer 40

d. Administer oxytocin (IM or IV) and lavage the uterus to facilitate removal ## Footnote Most texts state that the placenta in a mare is retained after greater than 3 hours post-parturition; therefore, this would be considered a retained placenta. Oxytocin, along with uterine lavage, will cause the uterus to contract and facilitate expulsion of the placenta. Strong physical traction on the retained placenta is generally considered contraindicated, as you may tear the placenta and leave remnants of it within the uterus, resulting in possible complications. Broad-spectrum antimicrobials are often administered to decrease the incidence of metritis but alone would not be appropriate.

Answer 41

c. Virus ## Footnote Equine infectious anemia is caused by a retrovirus that establishes a lifelong infection and causes cyclic anemia and abortions.

Answer 42

c. Eastern equine encephalomyelitis ## Footnote This question was not meant to be hard. Another cause of a viral encephalomyelitis which we also vaccinate for is western equine encephalomyelitis. The other diseases do not result in encephalomyelitis. Tetanus will cause a rigid paralysis due to binding of tetanus toxin to inhibitory receptors. Influenza will usually cause respiratory disease. Strangles will usually result in a raging lymphadenopathy with subsequent abscessation.

Answer 43

d. Neurologic signs associated with hyperammonemia and intestinal disease ## Footnote Ok, admittedly this is a tough question, but we do not want to make them too easy. Hyperammonemia has been associated with intestinal disease in horses. The exact cause of the neurologic signs and disease process is unknown, but it is presumed to result from excessive ammonia production within the intestinal tract. This overwhelms the ability of the liver to metabolize ammonia, and subsequently causes the development of encephalopathic signs, such as those reported in this question. Diarrhea is a common concurrent problem suggesting a possibility that overgrowth of ammonia producing bacteria causes an elevated blood ammonia. In regards to the other possible answers, hyponatremia can cause neurologic deficits if the sodium is very low (100-105 mEq/L), so the sodium of 124 mEq/L in this question rules that option out. The mild azotemia and hyperglycemia are unlikely to cause neurologic deficits and there is no other evidence to support hepatic disease.

Answer 44

a. Squamous cell carcinoma ## Footnote he most common tumor of the kidney in a horse is renal carcinoma.

Answer 45

b. Anemia ## Footnote Purpura hemorrhagica is a possible sequela of streptococcus equi infection exposure or vaccination. It develops from a Type III hypersensitivity resulting in immune complex deposition in blood vessel walls and vasculitis. Common clinical signs are as described in the question. This is a nonthrombocytopenic purpura (most horses will have a normal platelet count). Common findings include anemia, hyperproteinemia, hyperfibrinogenemia, hyperglobulinemia, and neutrophilia.

Answer 46

b. Notify the state and federal authorities The correct answer is notify the state and federal authorities. Vesicular stomatitis is a disease that must be reported to state and federal authorities. There is no specific treatment for the disease. Secondary infections should be treated symptomatically.

Answer 47

a. Inhibition of intestinal motility ## Footnote The correct answer is inhibition of intestinal motility. When xylazine is given at 1.1 mg/kg it decreases the motility of the distal jejunum, cecum, and pelvic flexure for over 2 hours. Xylazine can also transiently decrease cardiac output in a potentially hypovolemic horse with colic. Conversely, xylazine is a potent analgesic and can provide immediate relief to a horse with abdominal pain.

Answer 48

c. African Horse Sickness African horse sickness (AHS) is a viral disease of equids that is transmitted by insects, primarily Culicoides. Clinical signs of AHS typically develop 5-7 days after infection and begin with fever and conjunctivitis. Some animals may recover but many go on to develop the pulmonary and/or cardiac form of AHS. The pulmonary form consists of acute respiratory distress, coughing, sweating, and foaming from the nostrils; this form is usually fatal. The cardiac form consists of edema of the head and neck as well as abdominal pain and depression. A characteristic sign is swelling in the indentation above the eyes (also referred to as swelling of the supraorbital fossa). About 50% of animals with the cardiac form die from heart failure while the rest gradually recover after about one week. Glanders is a bacterial disease caused by Burkholderia mallei (previously known as Pseudomonas mallei). Burkholderia mallei causes 3 different forms of disease; nasal glanders, pulmonary glanders, and cutaneous glanders. The nasal form presents with high fever, loss of appetite and labored breathing with cough. The pulmonary form often develops over several months, beginning as a fever with dyspnea and cough. The cutaneous form develops over several months as nodules develop in subcutaneous tissue along the course of the lymphatics of the legs, costal areas, and ventrum. Surra is a trypanosomal disease causing primarily fever, weakness, and lethargy. Rift Valley Fever is a viral disease primarily of ruminants causing influenza-like signs and hepatic lesions.

Answer 49

e. Equine Motor Neuron Disease (EMND) The correct answer is EMND. This is a neurologic disease associated with dietary vitamin E deficiency which is believed to contribute to oxidative damage to the CNS. However, the precise pathophysiology is unknown. Retrospective studies have noted that horses with EMND are commonly housed on dry lots with little to no availability to pasture or good quality hay (perhaps contributing to low blood vitamin E concentrations). The clinical signs in this question are classic for EMND whereas horses afflicted with the other options do not typically demonstrate trembling or shifting of body weight.

Answer 50

e. Western Equine Encephalitis ## Footnote The keys to this question are that the horse is unvaccinated for WEE, has a progression of central nervous system signs over several days and characteristic CSF changes. Another reasonable differential would be rabies, particularly if the horse had not been vaccinated for it. Equine protozoal myeloencephalitis (or myelitis) can be seen at any age and is caused by Sarcocystis neurona. It should be suspected when a horse has asymmetric neurological signs as it is a multifocal disease of the central nervous system. Cervical vertebral malformations (Wobbler Syndrome) and degenerative myeloencephalopathy are diseases seen primarily in horses under a year of age. Degenerative myelopathy causes a symmetrical ataxia. Cerebellar abiotrophy is usually observed in foals which are less than one year of age, particularly 1-6 months of age. It is mostly seen in Arabian, Oldenburg, and Gotland breeds. There is no treatment and signs may be progressive. Diagnosis is based on a good history and clinical signs such as intention tremors, lack of a menace, hypermetria, and ataxia. Thiamine deficiency in horses usually occurs from ingestion of thiaminase-containing plants (bracken fern) and results in loss of condition and slight uncoordinated movements. If not treated, the disease may progress to cause twitching, tremors and seizures.

Answer 51

a. Opossum The correct answer is opossum. This is a must-know fact. The opossum is the definitive host for Sarcocystis, the causative agent of equine protozoal myelitis.

Answer 52

a. Anaplasmosis The correct answer is Anaplasmosis. The causative agent is Anaplasma marginale. The clinical signs are fairly straight forward, and you need to pick up on a couple key features. The fact that new adults are sick is one feature because cattle are resistant to clinical Anaplasmosis as calves. Also, it should be remembered that hemoglobinuria with Anaplasmosis is never seen because it is all extravascular hemolysis. Since there is no hemoglobinuria, leptospirosis, bacillary hemoglobinuria, and anthrax can be ruled out. Additionally, icterus with anthrax is not seen.

Answer 53

a. Lance and drain the abscess Antibiotics should only be used early on in the infection before abscessation or in cases where the abscess has become internal (bastard strangles).

Answer 54

a. Keep the horses in a dry and clean environment Scratches is a condition of chronic seborrheic dermatitis of the palmar/plantar aspect of the pastern. The condition is sometimes referred to by several other names including "grease heel", "dermatitis verrucosa", "dew poisoning" and "mud fever". It is not specific to the underlying infectious cause but the condition is generally associated with horses kept in wet or muddy environments. Treatment involves removing the horse from the wet environment, clipping the surrounding hair, and gently washing and cleaning the area with a disinfectant followed by careful drying. Topical ointments or astringent dressings may sometimes be used. The best prevention is to keep horses in a dry and clean environment and maintain good hygiene practices.

Answer 55

b. Neorickettsia risticii (Potomac Horse Fever) Neorickettsia risticii commonly causes diarrhea in the warmer summer months and is observed in horses stabled near bodies of water. Although a trematode vector is suspected, the exact pathogenesis remains an area of study. The treatment is oxytetracycline. While many causes of diarrhea can result in laminitis, PHF has been associated with laminitis frequently. Salmonella can also result in the clinical signs noted but is not restricted by season.

Answer 56

c. Aerosol Equine influenza is an orthomyxovirus and is spread in respiratory secretions of infected animals. It can be endemic in areas or spread as an epidemic because it is highly contagious.

Answer 57

d. Attempt to empty any grain out of the stomach via NG lavage of stomach, administer NSAIDs and start IV fluids ## Footnote The clinical presentation is consistent with a case of acute laminitis secondary to grain overload. Acute laminitis is frequently associated with excessive ingestion of carbohydrates, grazing of lush pastures, and/or excessive exercise. Acute laminitis more commonly affects the front feet but can affect all four. Local heat and pain are usually detected as well as bounding digital pulses. Pain may also manifest as tachycardia, muscle tremors, or sweating. The goals of treatment are to prevent further development of laminitis, reduce pain, and reduce other complications from laminitis. Acute laminitis is considered a medical emergency and treatment should be initiated as soon as possible. When a horse is suspected of grain overload, administration of mineral oil by stomach tube acts as a laxative and decreases absorption of toxic material from the gastrointestinal tract. Other recommended treatments include intravenous fluids, parenteral antimicrobials, anti-inflammatory drugs (such as flunixin meglumine or phenylbutazone), and hyperimmune serum or plasma. It is also recommended to place the horse in a stall with soft flooring. Other treatment considerations include heparin, phenoxybenzamine, and heart-bar shoeing. There are some practitioners who recommend cold packs but there is conflicting evidence that hot packs may be more beneficial. Corticosteroids are contraindicated.

Answer 58

a. Type I The newly formed type III collagen is eventually replaced by type I collagen; however, the replacement is never complete. This process takes between 8-11 months.

Answer 59

e. Third carpal bone Chip fractures of the radial carpal bone and radius are common and slab fractures are most common in the third carpal bone. Slab fractures of the central tarsal bone and third tarsal bone do occur but less frequently than in the carpus.

Answer 60

e. 25 ## Footnote Most equine practitioners should earn 25-30% of their gross intake; the average is about 26%. The national board examination will ask a few basic practice management questions that you should be prepared for.

Answer 61

b. Elevations in serum triglycerides, gamma glutamyl transpeptidase (GGT), and sorbital dehydrogenase (SDH) suggestive of hyperlipemia and hepatic lipidosis ## Footnote The most likely clinicopathologic changes that you would observe are elevations in serum triglycerides, GGT, and SDH. Unlike other larger sized horses, Miniature horses are susceptible to the development of hyperlipemia and hepatic lipidosis as a result of anorexia; the anorexia typically results from a primary disease, in this case mild colitis. Because of the negative energy balance, fats are mobilized in excess resulting in the opaque appearance of the serum. The other answers have one incorrect variable within the response: colitis is associated with metabolic acidemia, acute kidney injury is associated with hyperkalemia, and equine Cushing's syndrome is associated with hyperglycemia.

Answer 62

b. Duodenitis-proximal jejunitis ## Footnote Duodenitis-proximal jejunitis, also known as either anterior enteritis, or proximal enteritis best fits this case because of the characteristic reflux, fever, peritoneal fluid characteristics, rectal findings, the depression and relatively less pain than would be expected with an obstruction. The cause is still uncertain, but a relationship of this disease to positive cultures of reflux for Clostridium difficile has been found. Typically these cases are treated medically, which would include repeated decompression of the stomach, IV fluids, replacement of electrolyte deficiencies, analgesics and correction of any acid-base abnormalities.

Answer 63

b. Rotavirus ## Footnote The correct answer is rotavirus. Rotaviruses are the most common viral cause of diarrhea in foals. Rotavirus will destroy absorptive intestinal cells in the small intestine thus causing a malabsorptive diarrhea. As with almost all viral diseases, treatment is supportive.

Answer 64

a. Aminocaproic Acid ## Footnote Aminocaproic acid is the only anti-fibrinolytic medication listed that may promote hemostasis. Aminocaproic acid binds and inhibits plasminogen activation thereby promoting clot maintenance and stabilization. The other medications would be considered fibrinolytics (tPA) or anti-coagulants (LMWH, aspirin).

Answer 65

c. Flunixin meglumine and phenylbutazone ## Footnote The correct answer is flunixin meglumine and phenylbutazone. Simultaneous administration of two NSAIDS increases the likelihood of gastric ulceration.

Answer 66

d. Right side ## Footnote The correct answer is right side. Although this is not right 100% of the time, the fast phase of nystagmus tends to go away from the lesion. The direction of nystagmus is named after the fast phase. So be careful, this can get a little confusing. In addition, if this question had provided information as to which direction the head tilt and circling were occurring, you would be that much more confident in localizing your lesion (ex. right-side head tilt or circling would be a right-sided lesion). Sometimes you may have paradoxical vestibular disease, in which the lesion does not follow the rules, and the lesion is on the opposite side of what is expected; however, this is rare. This is usually caused by destruction of the cerebellopontine angle or flocculonodular lobe.

Answer 67

a. Abaxial Sesamoid Nerve Block First, you must determine that there is osteoarthritis of the pastern joint (proximal interphalangeal joint). Observe the periosteal bone proliferation and sclerosis along the medial side of the joint along with collapse of the medial joint space. Next, it is important to know what locations are blocked by the various perineural injections. You are likely to see at least one question on the board exam in regard to nerve blocks. The palmar digital nerve block typically blocks the palmar part of the foot; the abaxial block desensitizes the foot and proximal interphalangeal (pastern) joint; the low four point block desensitizes the foot, pastern and fetlock joint; and the subcarpal block desensitizes the metacarpal region and below. Thus, the lowest block that would likely desensitize the area in question is the abaxial sesamoid block.

Answer 68

d. Dentigerous cyst ## Footnote The correct answer is dentigerous cyst. This occurs as a result of having tooth germ tissue in the ear. Usually, a swelling at the base of the ear and observe a seromucoid discharge can be identified. Treatment is surgical removal of the tissue.

Answer 69

b. Gram negative facultative anaerobe ## Footnote The correct answer is gram negative facultative anaerobe. In horses, it primarily infects the cecum and proximal colon.

Answer 70

c. Cyanide toxicity ## Footnote The correct answer is cyanide toxicity. Cyanide does not allow hemoglobin to release oxygen, thus causing the cherry red lips. It is found in cherries, chokecherries, arrow grass, and Sudan grass. Large amounts must be consumed. There is a bitter odor of almonds to the GI tract with this toxicity. Treatment is sodium nitrate and sodium thiosulfate. Prognosis is poor due to the rapid onset. Carbon monoxide can cause cherry red mucous membranes but would not cause the almond smell.

Answer 71

d. Virus The correct answer is virus. Equine infectious anemia is caused by a retrovirus that establishes a lifelong infection and causes cyclic anemia and abortions.

Answer 72

c. Stallions and non-pregnant mares The correct answer is stallions and non-pregnant mares. Since the vaccine is modified live, there is a risk for clinical signs in under developed immune systems such as foals. Immunity will last for 1-3 years, and vaccinated horses cannot be distinguished from infected horses by serology.

Answer 73

c. At 5, 7, and 9 months of gestation ## Footnote The correct answer is at 5, 7, and 9 months of gestation. Failure to do this will result in an increased chance of abortion. The vaccine only provides immunity for 2-4 months making it necessary to booster every 2 months toward the end of gestation.

Answer 74

e. Arabian ## Footnote The correct answer is Arabian. This condition should be suspected in an Arabian horse with cerebellar disease. Signs usually develop after 6 months of age and vary in severity, but usually consist of ataxia, hypermetria, head tremors (intention tremors), and hyperreflexia.

Answer 75

c. Selenium The correct answer is selenium. The causes of oxidative denaturation of hemoglobin (Heinz body anemia) in horses include phenothiazines, methylene blue, acetylphenyl hydrazine, low molybdenum diet, rye grass diet, brassica family, onions, and wilted red maple leaves.

Answer 76

c. Venerally ## Footnote The correct answer is venereally. EVA may also be transmitted via aerosolized secretions. Most infections are asymptomatic in adults, but clinical signs may include fever, lethargy, anorexia, edema, oculo-nasal discharge, and petechia. In foals, severe respiratory distress, leukopenia, thrombocytopenia, and death after 12-24 hours can occur.

Answer 77

c. Shunting blood from the right atrium to the left atrium The correct answer is shunting of blood from the right atrium to the left atrium. The foramen ovale is a small slit that allows shunting between the right atrium and left atrium in the fetus. Once the foal is born, the lungs expand (right atrial pressure decreases) and the left atrium becomes a higher pressure system than the right. This higher pressure in the left atrium at birth forces the closure of the foramen ovale flap against the septum secundum and, in health, typically fusion of these tissues occurs to permanently close the foramen ovale. However, if the foramen ovale flap does not fuse, this leads to patency. In this case, the flap acts somewhat akin to a one-way valve so when the LA pressure is higher the flap is closed, but when the RA pressure is higher, blood can flow right to left. This occurrence (RA pressure \> LA pressure) may happen when the patient coughs, takes a deep breath or sneezes which increases the return of venous blood to the RA.

Answer 78

b. This conduction finding is common in racehorses and is unlikely to contribute to poor performance ## Footnote Second-degree atrioventricular block is commonly seen in athletic horses. First-degree and second-degree blocks are considered variations of normal in the horse and are usually associated with high vagal tone. Horses with second-degree atrioventricular block are NOT predisposed to electrical-mechanical disassociation. This is not a cause of poor performance or a concern in horses because high vagal tone is overcome by sympathetic tone during exercise.

Answer 79

c. Most horses improve with treatment, but relatively few make a complete recovery This is a case of Equine protozoal myeloencephalitis. EPM can be tricky to diagnose because the clinical signs can be quite variable but the key findings are the "3 A's", namely asymmetry, ataxia, and atrophy. The onset of clinical signs are frequently gradual but rapid progression is seen in some cases. Differential diagnoses can include cervical vertebral malformation, equine degenerative myeloencephalopathy, equine herpes myeloencephalitis, polyneuritis equi, and verminous myeloencephalitis. However, the asymmetric and multifocal signs as well as the horse's age and gradual onset of signs make EPM the most likely diagnosis. The prognosis for horses with EPM is often described as variable. Studies show that about 70% of treated horses will improve but only up to 25% recover completely and perform normally. In addition, a subset (5-20%) of horses may improve while undergoing treatment but then relapse when treatment is discontinued. It is unclear whether relapse represents reemergence or persistence of resistant parasite or re-exposure. Based on these features of EPM, the best answer choice of those listed is that most horses improve with treatment but relatively few make a complete recovery.

Answer 80

b. PCR of a guttural pouch wash for the S. equi M protein (SeM) gene Testing for Streptococcus equi subsp. equi can be complex. The 3 major tests are PCR, serology, and culture. PCR and serology both detect SeM which is an important virulence factor for the bacteria. Culture is best performed on Columbia CNA agar with 5% sheep or horse blood. While there are pros and cons to each test, the key to answering this question correctly is focusing on the issues of sensitivity and detecting carriers. PCR is approximately 3 times more sensitive than culture. In general, sampling the guttural pouch is a better way to detect carriers than the nasopharynx because it is where most carriers harbor the organism. Serology is the best test for assessing exposure but is not a good tool for detecting carriers. This is because antibodies may be elevated after an infection has been cleared or even after vaccination. It may also be falsely negative if an exposure was recent. To summarize the best uses of culture, PCR and serology: Culture is the gold standard for diagnosing a horse with an infection. PCR is best for detecting asymptomatic carriers, establishing infection status prior to or following transport, and to determine the success of elimination of S. equi from the guttural pouch. PCR cannot distinguish live DNA from dead DNA and may have false positives after a cleared infection. Using PCR in combination with culture may be helpful in such an instance. Serology is best for determining exposure and the need for vaccination as well as for supporting diagnoses of S equi associated purpura hemorrhagica or of bastard strangles.

Answer 81

d. Clostridium piliforme The correct answer is Clostridium piliforme. This is a motile, filamentous, gram negative, spore forming bacterium. Of note, all Clostridia are categorized as gram positive organisms with the exception of Clostridium piliforme, which is gram negative (yes, Microbiology is confusing). Clinical signs associated with Tyzzer's include depression, anorexia, coma, convulsions, and jaundice. Horses between 6 days and 6 weeks of age are affected; however, most are affected at 1-2 weeks. Affected foals will have elevated liver enzymes, marked hypoglycemia, and acidosis.

Answer 82

c. Squamous cell carcinoma

Answer 83

c. Pseudomonas ## Footnote The correct answer is Pseudomonas. Pseudomonas is the most common agent causing bacterial keratitis in the horse. The gram negative cytology provides further evidence that it is the likely culprit. Staphylococcus can cause keratitis in horses but is gram positive. E. coli and Pasteurella are not agents that are commonly involved with keratitis in the horse.

Answer 84

a. Seasonal anestrus Mares are seasonal breeders and enter anestrus in the short-day months of late fall and winter. In anestrus, the ovaries are inactive with small follicles and no corpus lutea. During estrus, the uterus softens and multiple follicles form on the ovaries. During pregnancy, the uterus has good tone.

Answer 85

d. Papillomavirus is believed to play a role in the pathogenesis ## Footnote Sarcoids are one of the most common tumors in horses. They are considered non-metastatic tumors in virtually all cases. For this reason, small lesions are sometimes treated with benign neglect, but they are not expected to regress. More advanced lesions or tumors in certain sites do need to be treated more aggressively. Unfortunately, no single treatment is universally effective. Recurrence rates after surgical excision are approximately 50%. Although there is still controversy surrounding this issue, either bovine papillomavirus or an equine variant is thought by many to play a role in development of these tumors.

Answer 86

b. Topical imiquimod (Aldara) Aural plaques in horses are caused by papillomavirus and are mechanically spread by insects such as black flies. Lesions do not typically regress but a 2010 study (Veterinary Dermatology; 21(5) 503-509) showed that topical application of imiquimod cream was efficacious in causing resolution of the lesions. Environmental insect control is also a wise recommendation in this case but would not lead to regression of the lesions. Systemic antibiotics or glucocorticoids would not be effective against this viral lesion but glucocorticoids are sometimes used to control clinical signs (pruritus) seen concurrently with these lesions.

Answer 87

d. Premolar 1 The correct answer is premolar 1. This is also known as the wolf tooth and is commonly removed so that bits can be easily fitted to the horse's mouth. This tooth erupts at 5-6 months of age. Molar 1 does not erupt until about one year of age. The canine does not come in until 4-5 years of age. The first permanent incisor is seen at approximately 2.5 years of age.

Answer 88

a. Red maple leaves (Acer rubrum) ## Footnote The sclera appears icteric. In combination with the clinical signs, ingestion of Red maple leaves would result in these signs due to hemolysis and low oxygen content of the blood. Oak is toxic but causes diarrhea and abdominal pain, whereas Black walnut is associated with laminitis. Yellow star thistle causes nigropallidal encephalomalacia resulting in CNS signs.

Answer 89

e. Penicillin ## Footnote The only disadvantage is that procaine penicillin needs to be injected and the individual horse may become sore and needle shy.

Answer 90

d. Ampicillin The correct answer is ampicillin. Ampicillin is excreted by the kidneys and without hepatic metabolism. All other answer choices undergo extensive hepatic metabolism before being excreted.

Answer 91

b. Exposure or ingestion of eastern tent caterpillars ## Footnote The correct answer is exposure or ingestion of eastern tent caterpillars. The exact pathogenesis of MRLS is still unknown, but the presence of eastern tent caterpillars was strongly associated with the disease. Later, experimental studies in which pregnant mares were exposed to or fed eastern tent caterpillars resulted in early and late fetal loss.

Answer 92

c. Strangles ## Footnote Strangles is caused by Streptococcus equi. It is a highly contagious disease, especially to naive young animals.

Answer 93

c. 18 The horse has 18 pairs of ribs

Answer 94

a. Cranial nerves VII and VIII (left side); fracture of the basiphenoid bone The correct answer is damage to cranial nerves VII (facial nerve) and VIII (vestibular nerve) on the left side caused by fracture of the basisphenoid bone. This is a common injury when a fractious young foal rears up and falls backward on the poll. The basisphenoid bone becomes injured resulting in injury to cranial nerves VII and VIII. Damage to the facial nerve results in the muzzle deviation (opposite direction of the side of injury, in this case deviated to the right), ptosis of the left eye and drooping of the left ear. Damage to the vestibular nerve results in the head tilt.

Answer 95

c. Sarcoid The sarcoid comes in many forms and can be difficult to eliminate in many cases. Bovine papillomavirus types 1 and 2 are associated with this tumor of horses.

Answer 96

b. Bovine The correct answer is bovine. Haematobia irritans requires cattle feces to reproduce, although the adults will feed on horses, sheep, and goats as well. The flies spend all of their life cycle on the host except when reproducing and cannot fly much further than 10 miles off of the host.

Answer 97

e. Administer ivermectin twice annually, once in the early summer and again in the fall This case describes the appearance of the horse bot fly, Gasterophilus spp. Gasterophilus is frequently asymptomatic but treatment is recommended because bots can cause gastritis and frequently are a source of annoyance and stress to horses. In addition, the larval instars can cause stomatitis, and colic. The key to answering this question regarding optimal treatment and management is an understanding of the Gasterophilus life cycle. Gasterophilus undergoes complete metamorphosis, including three larval instars and only one generation is produced per year. The general cycle typically begins with the female ovipositing 150-1,000 eggs on a horse during the early summer months directly on single hairs of the horse's front legs (especially around the cannon bone area) as well as the abdomen, flanks, and shoulders. The eggs are approximately 1-2mm long and are pale to grayish yellow attached near the tip of the hair. The eggs develop into first instar larvae within five days and they are stimulated to emerge by the horse licking or biting at the fully developed eggs. The larvae then crawl to the mouth or are ingested and subsequently bury themselves in the tongue or gingiva and remain for approximately 28 days. The larvae molt to the second stage and move into the stomach. The second and later third stage larvae typically attach to the lining of the stomach in the non-glandular portion near the junction of the esophageal and cardiac regions where they remain immobile for the following 9 to 12 months. The third instar larvae are relatively large, between 1-2cm long with a rounded body, narrow, hooked mouthparts, and spines. The hooked mouthparts enable the larvae to securely attach to the lining of the stomach and intestinal tract. After the third instar larvae have matured, they detach from the gastrointestinal tract and pass from the horse's body in the feces. The larvae burrow into the soil or dried manure where they pupate and remain for the next one to two months. This stage of the life cycle occurs between late winter and early spring. Based on this life cycle, the recommended management protocol is typically to treat with an avermectin to control adults and all larval stages by administering in the early summer, shortly after any eggs are seen and again in the fall at the end of the botfly season. Such a control program will substantially reduce fly numbers.

Answer 98

b. The head, neck, and withers are the most commonly affected area ## Footnote The correct answer is the head, neck, and withers are the most commonly affected areas. Demodicosis in horses is a rare disease and is not typically pruritic in nature. A skin scraping is the diagnostic test of choice, and there is no satisfactory treatment for the disease. Amitraz can be used to treat dogs with Demodex, but it causes colic and death in horses.

Answer 99

c. 1.012 ## Footnote The correct answer is 1.012. Isosthenuria would be expected in any horse with chronic renal insufficiency that is causing azotemia. Isosthenuria is typically defined by a urine specific gravity of about 1.008-1.015.

Answer 100

a. Rest, phenylbutazone, and intra-articular injections of sodium hyaluronate ## Footnote Cases of osselets that are caught before the development of osteoarthritis often respond completely to medical management consisting of rest, anti-inflammatories (such as phenylbutazone) and intra-articular injections of sodium hyaluronate or polysulfated glycosaminoglycans (Adequan). Fetlock arthrodesis is reserved for more advanced fetlock injuries. Deep digital flexor tenotomy is used to treat certain cases of chronic laminitis. Palmar digital neurectomy is used to treat navicular disease and results in desensitization of the heel.

Answer 101

e. Chronic liver disease ## Footnote GGT is a marker of hepatobiliary disorders and cholestasis in large animals.

Answer 102

d. Pituitary pars intermedia dysfunction This disorder used to be called equine Cushing's. This condition is a result of hypertrophy, hyperplasia, and micro- or macroadenoma of the pituitary pars intermedia that secretes increased amounts of propiomelanocortin peptides. Adjacent pituitary tissues are compressed and secrete less of some other peptides. Data suggest that horses with this disease have hypothalamic dysfunction and decreased amounts of dopamine

Answer 103

d. Opisthotonos ## Footnote The correct answer is opisthotonos. Bracken fern contains thiaminase, leading to thiamine (vitamin B1) deficiency. Clinical signs include anorexia, weight loss, incoordination, convulsions, wide-based stance, opisthotonos, and death.

Answer 104

a. Onions ## Footnote The correct answer is onions. Onions can cause Heinz body anemia through oxidative damage to red blood cells and result in hemoglobinemia and hemoglobinuria.

Answer 105

b. 60 days The correct answer is 60 days. For this reason, a stallion with poor quality semen should be re-evaluated in 2 months before making a final judgment.

Answer 106

c. Carpus valgus ## Footnote This is one of the most common angular limb deformities that occurs in foals, usually as the result of asynchronous growth of the metaphyseal and epiphyseal growth plates.

Answer 107

d. Bacterial lipopolysaccharide ## Footnote The cell walls of all Gram negative bacteria contain varying amounts of lipopolysaccharide, which in turn varies in its potency to create adverse reactions in animals. The signals have evolved on monocytes and macrophages to warn the animal when a Gram negative bacterium has gained access. When the reaction to this signal is overzealous, a cascade of adverse physiologic reactions can occur.

Answer 108

b. Stallion positive for Qa and mare negative for Qa ## Footnote The correct answer is stallion positive for Qa and mare negative for Qa. For neonatal isoerythrolysis to occur, the mare must develop antibodies to the foal's red blood cell antigens. Aa and Qa are the two antigens most frequently implicated in this condition. For this condition to occur, the foal must inherit the Aa or Qa antigen from the stallion, and the mare must be negative for the antigen (if she was positive, meaning she has the Qa antigen on her RBCs, she would not make antibodies against it). Then, when the mare becomes exposed to the foal's red blood cell antigens, she makes antibodies. When she passes these antibodies to the foal through colostrum, an acute hemolytic event will occur in the foal. In most cases, the first time a mare has a foal with the antigen, she will not produce sufficient antibodies to cause severe damage to the foal. Therefore, this condition is usually seen in multiparous dams or in mares that have previously had a blood transfusion that exposed them to the red blood cell antigens.

Answer 109

a. Vesicular stomatitis ## Footnote None of the other choices have occurred in the US in many decades. VS is a rhabdoviral disease which occurs in cycles in the USA, Mexico and South America, and can affect cattle, horses, donkeys, mules and pigs. In addition to the mouth, lesions can occur on teats and interdigital areas as well. Morbidity can be high, but mortality is usually low. The NJ serotype has been found in the US every year. Both migratory grasshoppers and the plants they eat can be infected with VS virus. Biological vectors include the midge Culicoides sonorensis, sand flies, and black flies. This is a reportable disease.

Answer 110

c. Foal heat diarrhea The correct answer is foal heat diarrhea. Although any of these answers could be correct, sometimes this is all you have to go on for some exam questions. To answer this question you need to know at what time periods foals get what diarrhea and the severity. Foal heat diarrhea is mainly seen at the age of 7-14 days and is usually very mild in nature, making this the best answer choice. Rhodococcus equi will result in diarrhea in foals that are between the ages of 1-4 months; however, remember that this organism primarily causes respiratory disease, so look for that too. Clostridium perfringens Types A, B, and C will usually result in an acute to peracute diarrhea in foals, leaving most of them dead in 48 hours if treatment is not instituted. Primary lactose intolerance is rare in foals.

Answer 111

b. Right dorsal colitis ## Footnote The correct answer is right dorsal colitis. Concurrent renal medullary crest necrosis may also occur with NSAID toxicity.

Answer 112

b. Neomycin and polymyxin B and dexamethasone (Neo-Poly-Dex) ## Footnote The correct answer is Neo-Poly-Dex. This is an illustration of a melting ulcer. Any corneal ulcer, whether it is superficial or deep, can be perpetuated by steroid use. Steroids increase the protease activity causing the "melting"; therefore, one of the primary goals in managing corneal ulcers is to decrease protease activity by using EDTA and serum. Further, aggressive topical antibiotic use is essential. Tobramycin, gentamicin, neomycin-polymyxin B-bacitracin, among others are appropriate. Intravenous banamine is the drug of choice for ocular pain and inflammation in horses. Tropicamide is used for its mydriatic and cycloplegic effect because all animals with corneal ulcers have uveitis. Atropine is an alternative to tropicamide. It is important to note that, even though atropine has a longer duration of action than tropicamide, atropine must be used with extreme caution in horses as it may potentiate colic

Answer 113

d. Ergotism The correct answer is ergotism. Claviceps purpura is a parasitic fungus found on rye, oats, wheat, and Kentucky bluegrass. Its toxicity comes from alkaloids and causes vascular constriction, thrombosis, gangrene, and vomiting, colic, diarrhea, and constipation. Diagnosis is made by identifying ergot on the grain.

Answer 114

e. Day 25 The correct answer is day 20. By day 20-30 the vesicle forms as a ventral bulge and thinning to the side of the bifurcation of the uterus. The fetus is usually not palpable until about day 90-120. Ultrasound can be used to diagnose pregnancy as early as 11-14 days. However, we want to know about "rectal palpation".

Answer 115

c. Ruptured prepubic tendon The correct answer is ruptured prepubic tendon. This tendon courses along the ventrum and provides the major support for all the structures in the equine abdomen. It can rupture in late pregnancy, especially in obese draft mares. This is usually preceded by ventral swelling. If such swelling is noted, preventative measures should be taken such as restricting activity and possibly slinging the abdomen to provide support. This condition is very painful to the mare and may affect the ability to increase intra-abdominal pressure during parturition. Assisted parturition by a veterinarian should be strongly considered. A body wall hernia may also result in similar signs as a ruptured prepubic tendon.

Answer 116

d. Respiratory acidosis with metabolic compensation caused by neonatal encephalopathy (hypoxic-ischemic encephalopathy) This is a more complicated question that requires evaluation of the entire case. First, recognize the foal's problem list includes: lethargy, hypoventilation, intermittent seizures as well as no suckle response. Next recognize that the arterial blood gas reveals a normal PO2 in a recumbent foal but hypercarbia (respiratory acidosis) with metabolic compensation. Based on these findings, the most likely cause in neonatal encephalopathy. This disease can arise from hypoxic conditions in utero or during parturition (dystocia, premature placental separation) resulting in a cascade of biochemical derangements within the body. Clinical signs include lethargy, failure to find and nurse from the udder, seizure activity, and in more severe cases damage to the gastrointestinal system and/or kidneys from hypoxia. Many foals are hypercapnic because the respiratory center within the CNS is not operating normal. There can be evidence of infection that complicates the presentation of some foals with neonatal encephalopathy, but in this case the CBC and rectal temperature are normal, making infectious diseases (bacterial meningitis, septicemia) less likely. You should have some knowledge of what normal arterial blood gas reference intervals are: pH 7.35-7.5; PO2 variable in venous blood; PCO2 around 40 mmHg, HCO3 24-30 mEq/L, iCa++ 1.4-1.8 mmol/L. This is a general range, with each species having slight changes to this range.

Answer 117

b. Cerebellar abiotrophy ## Footnote The correct answer is cerebellar abiotrophy. This is a condition seen primarily in Arabian foals and results in ataxia, dysmetria, head tremors (intention tremors), and hyperreflexia. Signs typically develop around 6 months of age.

Answer 118

d. Foal heat diarrhea The correct answer is foal heat diarrhea. The exact cause of this is unknown and is termed foal heat diarrhea because of the relationship to the occurrence of post foaling estrous in the mare. However, we don't believe it is caused by estrous. It is possible that consumption of grain and hay may play a role in altering the gastrointestinal flora such that diarrhea develops. Foal heat will occur at 7-14 days of age. S. vulgaris and S. westeri will usually cause diarrhea later on in life due to their life cycles. Cryptosporidium may be a cause of diarrhea, but it is also found in healthy foals.

Answer 119

b. 1.012 ## Footnote The correct answer is 1.012. Isosthenuria would be expected in any horse with chronic renal insufficiency that is causing azotemia. Isosthenuria is typically defined by a urine specific gravity of about 1.008-1.015.

Answer 120

a. Administer oxytocin (IM or IV) and lavage the uterus to facilitate removal

Answer 121

d. Daily catheterization and lavage of the pouches Irrigation should use saline or saline plus an appropriate and non-irritating antimicrobial drug. Systemic antimicrobial drugs are also used, but the hallmark of successful therapy is lavage and drainage. For inspissated pus or refractory cases, surgical drainage may be necessary.

Answer 122

b. Pulmonary abscesses The two horizontal lines represent fluid or pus capped by gas within cavitary lesions. In foals, this occurs most frequently with Rhodococcus equi pneumonia.

Answer 123

e. Osteochondrosis ## Footnote The correct answer is osteochondrosis. Physitis in young horses involves swelling around growth plates in long bones. Physitis is sometimes thought to be a component of osteochondrosis, but the other answer choices have been suggested to be causes of physitis.

Answer 124

a. Chronic use of furosemide, a diuretic ## Footnote Loop diuretics cause excessive amounts of potassium to be lost via the urine.

Answer 125

c. Culicoides ## Footnote The correct answer is Culicoides. Culicoides hypersensitivity, also referred to as sweet itch, occurs due to allergy to the saliva of the gnat. It recurs seasonally in the warmer months and tends to worsen with age. Typically, horses are pruritic and develop lesions on the poll, mane, and tail from self trauma, although ventral midline dermatitis can occur as well. More chronically, scarring can occur. Treatment is to decrease exposure to the gnat and to treat with steroids. Habronemiasis is a condition where the larvae of the stomach worm migrate and emerge creating granulomatous lesions, usually around the eye, male genitalia, or lower extremities. Inside the granulomas, you can find dead larvae. Haematobia irritans is a bigger problem in cattle than horses (they reproduce in cow feces) but can affect horses, especially ones that are near cattle. It typically causes ventral midline dermatitis with wheals with a central crust that progress to alopecia and ulceration with fairly focal lesions, rather than more diffuse lesions caused by Culicoides. Onchocerca can cause dermatitis in the horse due to hypersensitivity to dying microfilariae. Lesions include alopecia and scaling of the ventral midline, face, and pectoral region. Often, lesions are diamond shaped and there may be a "bull's eye" lesion on top of the head. Onchocerca is nonseasonal, in contrast to Culicoides hypersensitivity, and variably pruritic. Ocular lesions can also occur with Onchocerca including uveitis, conjunctivitis, and keratitis. Lastly, Hypoderma is also a bigger problem in cattle but can occur in horses and typically creates nodules on the dorsum that have a pore on top.

Answer 126

b. Premolar 1 ## Footnote The correct answer is Premolar 1. For some reason it is commonly confused as being a canine tooth.

Answer 127

a. Intravenous fluids ## Footnote The correct answer is intravenous fluids. DSS, mineral oil, and fiber supplementation will likely not benefit a horse with diarrhea. There is no described infection, so antibiotics are not indicated at this time. IV fluids will help replace fluid losses associated with diarrhea and will help maintain a normal hydration state.

Answer 128

a. Usually performed to the left of midline The correct answer is usually left of midline. It is not recommended to perform an abdominal paracentesis to the left of midline as you are more likely to hit an organ such as the spleen. It is usually performed just to the right of midline. All other choices are true about abdominal paracentesis in a horse.

Answer 129

d. Meconium impaction The correct answer is meconium impaction. This occurs in neonatal foals, typically within the first 24 hours of birth, and results in tenesmus and variable degrees of colic. Acetylcysteine will cleave disulfide bonds in mucoproteins of meconium impactions and help break them down.

Answer 130

a. II, VII, IX, X ## Footnote The correct answer is II, VII, IX, X. These are the vitamin K-dependent coagulation factors. Warfarin is an inhibitor of vitamin K and interferes with hepatic synthesis of these factors.

Answer 131

a. Hypoproteinemia ## Footnote The correct answer is hypoproteinemia. The expected findings in a horse with blood loss are anemia (normocytic, normochromic), hypoproteinemia, and responsive bone marrow.

Answer 132

b. Monensin The correct answer is monensin. Monensin is a commonly used coccidiostat in feedstuff of cattle. This ionophore is highly toxic to horses (the toxic dose for hoses is 10 to 15 times less than for cattle) and will result in cardiomyopathy and myocardial necrosis. Unfortunately, there is no quick and easy antidote, and treatment usually consists of trying to empty the intestinal tract by using mineral oil, activated charcoal, and fluid therapy. Lasalocid and salinomycin are also ionophores that you might worry about, but monensin is much more toxic to horses. Selenium and copper are usually added to feedstuffs as a result of being deficient in the soil. Lack of supplementation with these minerals may result in cardiovascular disease, such as white muscle disease with selenium deficiency, and excessive bleeding in aged parturient mares with copper deficiency. One way of determining prognosis is to evaluate the horse's fractional shortening via echocardiography. Normally the fractional shortening is 30-40%; if you calculate fractional shortening to less than 20%, the prognosis is poor.

Answer 133

a. Decreased cardiac output ## Footnote The correct answer is decreased cardiac output. In an event of acute blood loss in a horse, catecholamines induce vasoconstriction and increased cardiac output. Antidiuretic hormone release causes water and sodium resorption in the kidney. Splenic contraction occurs to inject stored erythrocytes into circulation.

Answer 134

d. Anaplasma phagocytophilum infection ## Footnote Based on the clinical signs (fever, lethargy, tachycardia and limb edema), CBC results (leukopenia, neutropenia, thrombocytopenia) and microscopic observation of a morula within the neutrophil, the correct answer and diagnosis is Anaplasma phagocytophilum infection. Diagnosis can be supported via PCR assays. Anaplasmosis (formerly Ehrlichi equi) infects primarily neutrophils and form inclusion bodies which consists of one or more coccobacillary organisms within these cells, known as morula. The complete pathogenesis of this disease is not fully elucidated but the organism is spread via tick bites. Other clinical signs that may be associated with this disease include petechiation, icterus and ataxia. The drug of choice for this disease is...(think about it for a second)...you got it...oxytetracycline.

Answer 135

a. Administer oxytocin (IM or IV) and lavage the uterus to facilitate removal Most texts state that the placenta in a mare is retained after greater than 3 hours post-parturition; therefore, this would be considered a retained placenta. Oxytocin, along with uterine lavage, will cause the uterus to contract and facilitate expulsion of the placenta. Strong physical traction on the retained placenta is generally considered contraindicated, as you may tear the placenta and leave remnants of it within the uterus, resulting in possible complications. Broad-spectrum antimicrobials are often administered to decrease the incidence of metritis but alone would not be appropriate.

Answer 136

c. Pass a nasogastric tube ## Footnote The correct answer is to pass a nasogastric tube. It is crucial to do this, as horses are unable to vomit due to high lower esophageal sphincter tone. By passing the tube, you will allow reflux and relieve life-threatening gastric pressure. Sedation is important to help provide relief; however, gastric rupture will kill the horse first.

Answer 137

c. Administration of non-steroidal anti-inflammatory medications. For examples flunixin meglumine, is a risk factor for the development of C. difficile enterocolitis ## Footnote The correct answer is NSAID treatment is a risk factor for the development of C. difficile enterocolitis. Remember all the other answers are correct, so hopefully you can take away some of these important facts from this question. Risk factors for the development of disease include antibiotic treatment and hospitalization, but does not include administration of NSAIDs.

Answer 138

b. Topical tobramycin The correct answer is topical tobramycin. Tobramycin is an aminoglycoside and would be effective against most gram negative organisms, including Pseudomonas, which are the most common cause of bacterial keratitis. Cefazolin would be useful topically for a gram + infection. Systemic antibiotics would not penetrate to the site at levels that would be effective. Natamycin is an antifungal drug and would not be useful in this case of bacterial keratitis.

Answer 139

c. Culture the discharge for bacteria The correct answer is to culture the discharge for bacteria. The most likely diagnosis for this horse is equine strangles. Strangles most commonly affects younger horses (\<5 years of age), but can cause disease in any age horse. The etiologic agent of this disease is Streptococcus equi subsp. equi. The diagnostic test of choice to confirm this is bacterial culture. While awaiting culture results, the horse should be separated from any other horses, as strangles is highly contagious to other horses. Antibiotic therapy is controversial and thought to lengthen the course of disease rather than shorten it when given at this stage; also, it may possibly interfere with the natural immunity acquired from natural infection. Strangles is a reportable disease.

Answer 140

b. Ethmoid hematoma ## Footnote The correct answer is ethmoid hematoma. An ethmoid hematoma is a progressive and locally destructive mass that resembles a tumor but is not truly neoplastic. The most common clinical sign is mild, persistent, spontaneous, intermittent epistaxis that can be unilateral or bilateral. Warfarin is not as likely in this horse due to the recurrent nature of the condition and the fact that it is unilateral. Exercise-induced pulmonary hemorrhage actually causes epistaxis only about 10% of the time. Also, since the bleeding is pulmonary in origin, the epistaxis would likely be bilateral. Epistaxis with this condition also occurs immediately after exercise, which was not reported in this horse. Purpura hemorrhagica is a vasculitis that results from a type III immune complex hypersensitivity after a streptococcus equi infection. This leads to vasculitis, and the main clinical signs are petechia and ecchymoses of mucous membranes.

Answer 141

d. Upward patellar fixation Upward patellar fixation causes the gait described above. Any horse that has the hind limb in rigid extension and is unable to flex it should be suspected of having this problem. One condition that can mimic this gait is luxation of the coxofemoral joint which can lead to an inability to flex the hind limb but this can be distinguished clinically because the limb will not be extended. Normally, when horses are standing and resting their hindlimbs, the patella elevates to the top of the femoral trochlea, and the medial patellar ligament hooks over the medial ridge of the trochlea, locking the joint and allowing the horse to rest the limbs. To flex the stifle again, the quadriceps femoris muscle contracts, lifting the medial patellar ligament free of the medial trochlear ridge allowing the patella to return to its working position. When something prevents the horse's ability to release the stifle, the condition is known as upward patellar fixation (also called "upward fixation of the patella" or "locked stifle"). Most cases of upward patellar fixation can be managed conservatively (exercise (physical therapy), improved body condition). In severe and unresponsive cases, surgery to cut the medial patellar ligament is an option. Stringhalt is involuntary flexion of the hindlimb and is usually bilateral. The problem in this case is rigid extension. Stringhalt is treated with lateral digital extensor tenectomy. Gonitis is a term indicating stifle arthritis. It is nonspecific to the underlying cause and could be due to osteochondrosis, ligament injury, or some other problem. Upward patellar fixation and its consequences could be referred to as gonitis but this is a less specific diagnosis in this case. Jack spavin is a lay term for cunean bursitis or irritation of the cunean tendon as a result of bone growth on the medial hock. Thoroughpin is the term for effusion of the tarsal sheath (sheath of the deep digital flexor).

Answer 142

a. Notify the state and federal authorities ## Footnote The correct answer is notify the state and federal authorities. Vesicular stomatitis is a disease that must be reported to state and federal authorities. There is no specific treatment for the disease. Secondary infections should be treated symptomatically.

Answer 143

b. It heavily predisposes to vaginitis and endometritis ## Footnote The correct answer is it heavily predisposes to vaginitis and endometritis. Aspiration of air leads to contamination, and pneumovagina is the most common cause of genital infections in the horse. Pneumovagina is a common cause of infertility due to the high incidence of vaginitis, cervicitis, and endometritis in affected mares. The Caslick procedure can be used in cases of pneumovagina in mares.

Answer 144

e. Immediately ## Footnote The correct answer is immediately. Administration of 1500 IU results in immediate protection that will last for approximately 2-3 weeks. Administration of tetanus toxoid will provide protective titers 14 days after the second dose, when given 3-6 weeks apart.

Answer 145

d. Cerebellum ## Footnote The correct answer is cerebellum. The cerebellum is responsible for the coordination and regulation of range, rate, and strength of movement along with balance and posture. Clinical signs associated with cerebellar disease include intention tremors, hypermetria, hypometria, and ataxia. Mentation will be normal if the disease is strictly confined to the cerebellum.

Answer 146

e. Clostridial spores entering a deep puncture wound The correct answer is clostridial spores entering a deep puncture wound. The spore is found in the soil and in feces and requires entry through a deep wound to find an anaerobic environment. They then form their toxin and release it, where it is picked up by nerves and travels to the spinal cord.

Answer 147

b. Shunting of blood from the right atrium to the left atrium The correct answer is shunting of blood from the right atrium to the left atrium. The foramen ovale is a small slit that allows shunting between the right atrium and left atrium in the fetus. Once the foal is born, the lungs expand (right atrial pressure decreases) and the left atrium becomes a higher pressure system than the right. This higher pressure in the left atrium at birth forces the closure of the foramen ovale flap against the septum secundum and, in health, typically fusion of these tissues occurs to permanently close the foramen ovale. However, if the foramen ovale flap does not fuse, this leads to patency. In this case, the flap acts somewhat akin to a one-way valve so when the LA pressure is higher the flap is closed, but when the RA pressure is higher, blood can flow right to left. This occurrence (RA pressure \> LA pressure) may happen when the patient coughs, takes a deep breath or sneezes which increases the return of venous blood to the RA.

Answer 148

a. 66% ## Footnote The correct answer is 66%. At this point you begin to see isosthenuria due to a decreased ability to concentrate urine. Azotemia will be apparent at approximately 75% damage to the kidneys.

Answer 149

c. Rest, phenylbutazone, and intra-articular injections of sodium hyaluronate ## Footnote Cases of osselets that are caught before the development of osteoarthritis often respond completely to medical management consisting of rest, anti-inflammatories (such as phenylbutazone) and intra-articular injections of sodium hyaluronate or polysulfated glycosaminoglycans (Adequan). Fetlock arthrodesis is reserved for more advanced fetlock injuries. Deep digital flexor tenotomy is used to treat certain cases of chronic laminitis. Palmar digital neurectomy is used to treat navicular disease and results in desensitization of the heel.

Answer 150

c. Phenoxybenzamine ## Footnote The correct answer is phenoxybenzamine. Phenoxybenzamine is an alpha-adrenergic antagonist promoting vasodilation and restoration of blood flow to the digits. Prednisone is contraindicated in laminitis because corticosteroids are believed to induce the condition. Antibiotics are not indicated unless a secondary bacterial infection develops. Application of a horse shoe would not help and would be very painful in an already sensitive and painful condition. Other medications used to restore blood flow to the digits include acepromazine, isoxsuprine hydrochloride, dimethylsulfoxide (DMSO), heparin, and nitroglycerine.

Answer 151

a. Prevent free access to lush grass pastures ## Footnote Acute laminitis is commonly associated with excess carbohydrate intake. Grazing of lush pastures is an especially common precipitating cause in ponies. Laminitis is not associated with selenium deficiency or arthropod problems.

Answer 152

c. Tyzzer's disease ## Footnote The correct answer is Tyzzer's disease. This is the most likely cause because of the age of the foal and the acute nature of the disease. Tyzzer's disease is caused by Clostridium piliformis, which causes an acute necrotizing hepatitis. It affects only foals from about 1-6 weeks of age. Theiler's disease is a condition of adult horses. Clostridium novyi is rare in horses and seen much more in sheep and cattle. Herpesvirus can cause hepatitis but is usually seen at or very soon after birth.

Answer 153

c. Equine Degenerative Myeloencephalopathy (EDM) The horse in this question has clinical signs most consistent with EDM; cervical vertebral malformation (wobblers) is also a possibility, but was not provided as an answer. The cause of EDM is unknown, but this disease typically affects young horses (\< 2-3 years of age; but older horses can develop disease). Clinical signs are a result of diffuse neuronal fiber degeneration of various portions of the central nervous system. This disease has been associated with low serum vitamin E concentrations, suggesting that oxidative damage may play a role in the development of disease. EMND is typically associated with muscle tremors, shifting of weight while standing, muscle atrophy and recumbency. Botulism is associated with generalized muscle weakness. Cauda equina syndrome causes analgesia of the perineum. EPM can cause a range of clinical signs, but is typically with asymmetric neurologic deficits.

Answer 154

a. IV plasma ## Footnote The damaged bowel is leaking albumin out into the gut lumen, and the horse may develop other problems such as edema and poor healing ability if the protein levels are not boosted. The best way to do that in an animal with GI disease is by the IV route. Whole blood may raise the PCV to a level where sludging and circulatory problems develop in an already dehydrated horse. Another option to consider if plasma is not readily available is the use of synthetic colloidal solutions such as hetastarch.

Answer 155

c. Cantharidin ## Footnote The correct answer is cantharidin. The blister beetle is the organism known to make this toxin. The toxin commonly gets incorporated into alfalfa, and the beetles get killed when the hay is processed. Other toxic causes of colic include oleander, rhododendron, and nightshades.

Answer 156

d. Laminitis ## Footnote The correct answer is laminitis. Black walnuts contain Juglone (naphthoquinone) which results in laminitis. Do not use black walnuts for horse bedding. Black walnut shavings, photo courtesy of Krishona Martinson, University of Minnesota

Answer 157

c. Pyrrolizidine alkaloid toxicity ## Footnote The correct answer is pyrrolizidine alkaloid toxicity. The three histopathologic changes described are the classic changes seen with pyrrolizidine alkaloid toxicity. With Tyzzer's disease, you would see randomly distributed foci of necrosis and long slender rods in hepatocytes at the periphery of the necrotic foci. With chronic active hepatitis, histopathologic changes would be hepatocyte damage, variable fibrosis, inflammatory infiltration, and evidence of biliary hyperplasia with bile stasis.

Answer 158

d. Ears back ## Footnote The correct answer is ears back. During anestrus, a mare will typically reject a stallion's romantic interest. Other signs of rejection by a mare include striking and avoidance of a stallion. The other choices are all signs of estrus.

Answer 159

b. Purulent inflammation and gram positive cocci with large capsules ## Footnote The correct answer is purulent inflammation and gram positive cocci with large capsules. The causative agent of strangles is streptococcus equi ssp. equi which is a gram positive cocci with a large capsule. It causes suppurative abscessation and enlargement of the mandibular and retropharyngeal lymph nodes.

Answer 160

b. 65L To determine this answer you must figure out the deficit and calculate the horse's maintenance needs. The deficit is 35L (deficit x BW). Maintenance needs for a horse is approximately 60ml/kg/day. In this case, 30L. Adding the deficit and maintenance fluids together yields a total of 65 liters.

Answer 161

a. Administer ivermectin twice annually, once in the early summer and again in the fall This case describes the appearance of the horse bot fly, Gasterophilus spp. Gasterophilus is frequently asymptomatic but treatment is recommended because bots can cause gastritis and frequently are a source of annoyance and stress to horses. In addition, the larval instars can cause stomatitis, and colic. The key to answering this question regarding optimal treatment and management is an understanding of the Gasterophilus life cycle. Gasterophilus undergoes complete metamorphosis, including three larval instars and only one generation is produced per year. The general cycle typically begins with the female ovipositing 150-1,000 eggs on a horse during the early summer months directly on single hairs of the horse's front legs (especially around the cannon bone area) as well as the abdomen, flanks, and shoulders. The eggs are approximately 1-2mm long and are pale to grayish yellow attached near the tip of the hair. The eggs develop into first instar larvae within five days and they are stimulated to emerge by the horse licking or biting at the fully developed eggs. The larvae then crawl to the mouth or are ingested and subsequently bury themselves in the tongue or gingiva and remain for approximately 28 days. The larvae molt to the second stage and move into the stomach. The second and later third stage larvae typically attach to the lining of the stomach in the non-glandular portion near the junction of the esophageal and cardiac regions where they remain immobile for the following 9 to 12 months. The third instar larvae are relatively large, between 1-2cm long with a rounded body, narrow, hooked mouthparts, and spines. The hooked mouthparts enable the larvae to securely attach to the lining of the stomach and intestinal tract. After the third instar larvae have matured, they detach from the gastrointestinal tract and pass from the horse's body in the feces. The larvae burrow into the soil or dried manure where they pupate and remain for the next one to two months. This stage of the life cycle occurs between late winter and early spring. Based on this life cycle, the recommended management protocol is typically to treat with an avermectin to control adults and all larval stages by administering in the early summer, shortly after any eggs are seen and again in the fall at the end of the botfly season. Such a control program will substantially reduce fly numbers.

Answer 162

a. Osselets ## Footnote Osselets are inflammation of the periosteum on the dorsal distal epiphyseal surface of the third metacarpal bone and fetlock joint. As in this case, they are often (but not always) bilateral. Osselets typically begin from chronic stress injury to the front fetlock(s) from repeated concussive forces during racing and hard training. Horses with long or upright pasterns may be predisposed. The major clinical signs are increasing lameness and a short choppy gait. Thickening and soreness of the fetlock are also frequently seen. Early diagnosis and intervention is important because once the condition progresses to osteoarthritis, the prognosis is much worse. If recognized early and treated with rest, anti-inflammatory medications, and intra-articular sodium hyaluronate injections, many horses can recover completely. None of the other choices listed are associated with the fetlock. Low ringbone is osteoarthritis of the distal interphalangeal (coffin) joint. High ringbone is osteoarthritis of the proximal interphalangeal (pastern) joint. Sidebones are ossification of the collateral (alar) cartilages of P3. Navicular syndrome affects the heel.

Answer 163

b. Trim away necrotic hoof material, apply antiseptic products, apply a bandage, and educate the client on proper hygiene ## Footnote The correct answer is to trim away necrotic hoof material, apply antiseptic products, apply a bandage, and educate the client on proper hygiene. The horse has thrush, a condition often caused by Fusobacterium necrophorum in horses. The condition is usually caused by unsanitary conditions, poor foot care, and lack of exercise. Systemic antibiotics and corticosteroids are usually unnecessary.

Answer 164

d. PCR of a guttural pouch wash for the S. equi M protein (SeM) gene Testing for Streptococcus equi subsp. equi can be complex. The 3 major tests are PCR, serology, and culture. PCR and serology both detect SeM which is an important virulence factor for the bacteria. Culture is best performed on Columbia CNA agar with 5% sheep or horse blood. While there are pros and cons to each test, the key to answering this question correctly is focusing on the issues of sensitivity and detecting carriers. PCR is approximately 3 times more sensitive than culture. In general, sampling the guttural pouch is a better way to detect carriers than the nasopharynx because it is where most carriers harbor the organism. Serology is the best test for assessing exposure but is not a good tool for detecting carriers. This is because antibodies may be elevated after an infection has been cleared or even after vaccination. It may also be falsely negative if an exposure was recent. To summarize the best uses of culture, PCR and serology: Culture is the gold standard for diagnosing a horse with an infection. PCR is best for detecting asymptomatic carriers, establishing infection status prior to or following transport, and to determine the success of elimination of S. equi from the guttural pouch. PCR cannot distinguish live DNA from dead DNA and may have false positives after a cleared infection. Using PCR in combination with culture may be helpful in such an instance. Serology is best for determining exposure and the need for vaccination as well as for supporting diagnoses of S equi associated purpura hemorrhagica or of bastard strangles.

Answer 165

d. Culicoides hypersensitivity The correct answer is Culicoides hypersensitivity. Culicoides hypersensitivity is extremely pruritic and is also known as "sweet itch". Horses can be affected on their ventrum or dorsum, depending on the species of the fly. The horse develops a type 1 hypersensitivity to the flies' salivary antigens and develops excoriations, alopecia, and thickened skin as a result of scratching. The flies are more prevalent during the warmer seasons and are most active during dusk and dawn. Treatment includes controlling the fly population. Stabling the horses at dusk is often helpful because the flies rarely enter barns. Insecticides, stable blankets, and fans for circulating air in the stables may also be useful. The extreme pruritus and seasonality of the clinical signs is often enough to differentiate the Culicoides hypersensitivity from other skin diseases. Onchocerciasis is vectored by Culicoides, but is not seasonal and is not nearly as pruritic. Mosquitoes can be an annoyance and, more importantly, are vectors for more serious diseases such as the equine encephalitides. Tabanus flies and Chrysops flies cause pain to horses by lacerating them with their mouth parts to feed on their oozing blood. They do not cause pruritus and can be differentiated by their large, robust size.

Answer 166

b. Chorioptes equi ## Footnote The correct answer is Chorioptes equi. Chorioptes is a mange mite that is usually found around the foot and fetlock. It causes a pruritic dermatitis that can cause the formation of papules, crusts, thickened skin, as well as alopecia. The mites are often found in the feathered hair around the fetlocks of draft horses. As with other mites, ivermectin is the treatment of choice. Culicoides, Haematobia irritans (the Horn fly) and onchocerciasis often cause dermatitis at the ventral midline of horses.

Answer 167

c. Scratches ## Footnote Scratches is a condition of chronic seborrheic dermatitis of the palmar/plantar aspect of the pastern. The condition is sometimes referred to by several other names including "grease heel", "dermatitis verrucosa", "dew poisoning" and "mud fever". It is not specific to the underlying infectious cause but the condition is generally associated with horses kept in wet or muddy environments. Summer sores are caused by Habronema spp. and Draschia spp. stomach worms of the horse. The larvae in feces are ingested by the maggots of flies, and the flies can deposit them at susceptible moist skin areas, damaged skin areas, or mucous membranes where the larvae cause an eosinophilic granuloma as a reaction to their migration. Sweet itch results from a Type 1 allergic reaction to Culicoides spp. Clinical signs of sweet itch are usually in the form of self-trauma due to pruritus. Sweeney is the common name for shoulder atrophy in the horse. The muscle atrophy is caused by damage to the suprascapular nerve which innervates to the infraspinatus and supraspinatus muscles. Ringbone refers to osteoarthritis or bony exostosis in the pastern (high ringbone) or coffin (low ringbone) joints.

Answer 168

d. Vesicular stomatitis The correct answer is vesicular stomatitis. Vesicular stomatitis is characterized by vesicle lesions on the tongue, inside of the mouth, teats, and feet. Besides horses, cattle, sheep, goats, and pigs are susceptible to the disease. The disease is differentiated from the others listed because horses are not naturally susceptible to the other diseases. The absence of papules and pustules allows us to differentiate vesicular stomatitis from horsepox.

Answer 169

e. Haematobia ## Footnote The correct answer is Haematobia. Haematobia irritans is a bigger problem in cattle than horses (they reproduce in cow feces) but can affect horses, especially ones that are near cattle. It typically causes ventral midline dermatitis with wheals with a central crust that progress to alopecia and ulceration with fairly focal lesions, rather than more diffuse lesions caused by culicoides. Onchocerca can cause dermatitis in the horse due to hypersensitivity to dying microfilariae. Lesions include alopecia and scaling of the ventral midline, face, and pectoral region. Often lesions are diamond shaped, and there may be a ""bull's eye"" lesion on top of the head. Onchocerca is nonseasonal, in contrast to culicoides hypersensitivity, and variably pruritic. Ocular lesions can also occur with Onchocerca including uveitis, conjunctivitis, and keratitis. Culicoides hypersensitivity, also referred to as sweet itch, occurs due to allergy to the saliva of the gnat. It recurs seasonally in the warmer months and tends to worsen with age. Typically, horses are pruritic and develop lesions on the poll, mane, and tail from self trauma, although ventral midline dermatitis can occur as well. More chronically, scarring can occur. Treatment is to decrease exposure to the gnat and to treat with steroids. Habronemiasis is a condition where larvae of the stomach worm that emerge from flies feeding on pre-existing wounds or genitalia or eyes, then migrate into the tissue and cause a granulomatous reaction. Inside the granulomas, you can find dead larvae. Lastly, Hypoderma is a bigger problem in cattle but can occur in horses and typically creates nodules on the back that have a pore on top.

Answer 170

a. Anhidrosis ## Footnote Anhidrosis is the inability to sweat, which can be fatal if not addressed. The cause is unknown. It tends to occur in hot humid climates, and may occur in horses raised in the climate, or more commonly, horses brought into the climate. The most successful treatment is to move the horse back to a more favorable climate.

Answer 171

d. Hyperosmolality and decreased circulating blood volume The correct answer is hyperosmolality and decreased circulating volume. In the horse, as in other species, ADH increases renal water reabsorption and urine osmolality by increasing permeability of the collecting tubules. Osmoreceptors in the hypothalamus detect subtle changes in plasma osmolality. If osmolality rises, you will hope to see ADH secretion so that the urine excreted would be more concentrated. The same is true if circulating volume decreases; thus, a lesser volume of water would be lost. When ADH secretion does not occur or if the kidneys are unable to respond to ADH, this is likely diabetes insipidus, and animals will be very polyuric, polydipsic and have extremely dilute urine.

Answer 172

b. Scents are moved to the vemeronasal organ The flehmen response, as described in the question, helps animals trap pheromone scents in the vomeronasal organs (VNOs) so they can be analyzed more closely. Pheromones are the chemical signals emanating from other animals. When a horse draws in an organic odor, he curls up his lip to temporarily close the nasal passages and hold the particles inside. The upward head tilt seems to help the airborne molecules linger in the VNOs, which are located under the floor of the horse's nasal cavity. While sex pheromones are the most common flehmen trigger, they are not the only ones, and the response itself does not indicate sexual interest.

Answer 173

c. St. John's wort This image shows a horse with skin sloughing due to cutaneous photosensitization. St. John's wort acts as a primary photosensitizer and can lead to photophobia, conjunctivitis, sloughed skin, and icterus. Blue-green algae cause sudden death. Slaframine causes hypersalivation and cantharidin causes colic.

Answer 174

a. Immue suppressive doses of corticosteoids ## Footnote The correct answer is immune suppressive doses of corticosteroids. Pemphigus foliaceus is an autoimmune disease in which antibodies are formed against the intercellular adhesin proteins. In horses, this disease causes crusting lesions of the head, limbs, and ventrum. Definitive diagnosis is found on biopsy of the skin showing acantholysis. There are two forms of the disease in horses. The juvenile form may result in spontaneous remission and carries a good prognosis. The adult form of the disease carries a worse prognosis.

Answer 175

d. Pituitary tumor ## Footnote The correct answer is pituitary tumor. Equine Cushing's disease is usually due to a pituitary adenoma of the pars intermedia secreting ACTH and leading to increased cortisol secretion from the adrenal glands.

Answer 176

a. Small colon impactions ## Footnote The correct answer is small colon impactions. Just a fun fact that is good to know.

Answer 177

a. Hepatotoxicity The correct answer is hepatotoxicity. Ototoxicity, nephrotoxicity, and vestibulotoxicity have all been associated with aminoglycoside use. An example of an aminoglycoside is gentamicin or amikacin.

Answer 178

d. Pyrrolizidine alkaloid The correct answer is pyrrolizidine alkaloid. The clinical signs described are typical for pyrrolizidine alkaloid toxicity. Consumption of this plant typically results in abnormalities in hepatic cell division; thus resulting in large hepatocytes known as megalocytosis.

Answer 179

d. Immature hippomane formation ## Footnote A premature foal is typically defined as a foal born before 320 days of gestation and demonstrating physical characteristics such as a short silky hair coat, soft pliant ears, laxity of the flexor tendons, a soft muzzle, and incomplete ossification of the carpal and tarsal bones. The hippomane is not part of the fetal anatomy but is the collection of cellular material and secretions found within the allantoic fluid.

Answer 180

a. Furosemide In this instance, the discharge is blood, with the most likely diagnosis being exercise-induced pulmonary hemorrhage (EIPH). One of the most commonly administered medications for EIPH is furosemide, which seems to decrease the incidence or lessen the severity of bleeding. The exact mechanism by which this occurs is not completely known but may be associated with reduced pulmonary capillary pressure.

Answer 181

d. Cerebellar abiotrophy The correct answer is cerebellar abiotrophy. The cerebellum is responsible for the coordination and regulation of range, rate, and strength of movement along with balance and posture. Clinical signs associated with cerebellar disease include intention tremors, hypermetria, hypometria, and ataxia. In addition, weakness is not observed with cerebellar abiotrophy. Mentation will be normal if the disease is strictly confined to the cerebellum. The key clinical sign not observed in this question is intention tremors. The clinical signs and presentation are definitely compatible with equine degenerative myeloencephalopathy, cervical vertebral myelopathy, and occipito-atlanto-axial malformation (OAAM). Computerized tomography (or radiography) is needed to rule in or rule out cervical vertebral myelopathy and OAAM. OAAM is relatively rare, but is most frequently observed in Arabian foals. These foals may be born dead, or may develop ataxia at several months of age. Histopathologic examination is the only way to definitively diagnose equine degenerative myeloencephalopathy (lesions in caudal brainstem nuclei and spinal cord).

Answer 182

c. Imidocarb The correct answer is imidocarb.

Answer 183

d. 1.012 The correct answer is 1.012. Isosthenuria would be expected in any horse with chronic renal insufficiency that is causing azotemia. Isosthenuria is typically defined by a urine specific gravity of about 1.008-1.015.

Answer 184

d. Bacterial lipopolysaccharide he cell walls of all Gram negative bacteria contain varying amounts of lipopolysaccharide, which in turn varies in its potency to create adverse reactions in animals. The signals have evolved on monocytes and macrophages to warn the animal when a Gram negative bacterium has gained access. When the reaction to this signal is overzealous, a cascade of adverse physiologic reactions can occur.

Answer 185

d. Sorbitol Dehydrogenase (SDH) and Gamma Glutamyl Transferase ## Footnote You have to read the possible answers carefully in this question and recall which enzymes are liver-specific in the horse. In this instance, SDH and GGT are both liver-specific; SDH is found in the liver of all animals. An increase in serum SDH concentration suggests hepatocellular injury. Elevation in serum GGT is predominately associated with biliary epithelial cells and is also liver-specific. The other enzymes listed may be increased with liver disease but may also arise from bone (ALP) or muscle (ALT, AST).

Answer 186

b. Administration of non-steroidal anti-inflammatory medications. For example, flunixin meglumine, is a risk factor for the development of C. difficile enterocolitis The correct answer is NSAID treatment is a risk factor for the development of C. difficile enterocolitis. Remember all the other answers are correct, so hopefully you can take away some of these important facts from this question. Risk factors for the development of disease include antibiotic treatment and hospitalization, but does not include administration of NSAIDs.

Answer 187

a. Large colon volvulus The correct answer is large colon volvulus. Typically, horses with this problem demonstrate rapid onset of severe unrelenting pain and often occurs in postpartum broodmares. Gas distension of the colon may be significant and result in respiratory compromise because the distended colon presses on the diaphragm. Gastric reflux may not be present as the small intestine may not be obstructed in this process. This is a surgical emergency; if surgery or necropsy is performed, the volvulus is typically located at the mesenteric attachment of the colon to the dorsal body wall. Because of the rapid onset, the prognosis is guarded to poor in many cases.

Answer 188

d. Erythromycin Erythromycin is often used in combination with rifampin. Others used are clarithromycin or azithromycin.

Answer 189

b. 6 days The correct answer is 6 days. Estrus in a mare can last 2-10 days but, on average, is 6 days long. The mare is a polyestrous animal from the beginning of spring through summer. The estrous cycle's duration lasts 19-26 days.

Answer 190

a. Conscious proprioceptive deficits of the pelvic limbs The correct answer is conscious proprioceptive deficits of the pelvic limbs. Usually the CP deficits will be on the side of the lesion. So you can expect to see right-sided CP deficits on a right-sided central vestibular lesion. Head tilt, facial nerve paralysis, and nystagmus are non-specific signs of vestibular disease. However, they do help you determine on which side the lesion is located. Quick note: if there are multiple cranial nerves paralyzed then you should start thinking this could be central. A right sided head tilt, right sided nerve paralysis, and nystagmus with the fast phase to the left will indicate a right-sided lesion. Abnormal mentation or seizures along with other vestibular disease signs would imply central vestibular disease.

Answer 191

c. Equine protozoal myeloencephalitis The correct answer is equine protozoal myeloencephalopathy. If at any time you observe vague asymmetric/multifocal neurologic clinical signs with focal muscle atrophy, this disease should be your top differential. Other potential clinical signs include hyporeflexia, spasticity, localized areas of sweating, cerebellar signs, head tilt, facial paralysis, circling, dysphagia, and blindness. EPM is caused by Sarcocystis neurona which is a protozoal organism that migrates randomly through the spinal cord and brain. This will result in damage of both white and gray matter. Cauda equina neuritis is an inflammation of the nerve roots (usually the cauda equina but sometimes cranial nerves) which results in lower motor neuron signs. You may see paresis and paralysis. Clinical signs include chewing the tail head, hypotonic anus, fecal retention, urinary incontinence (see urine scalding of the thighs), and hindlimb ataxia. Unfortunately, there is no good treatment. There are two forms of cervical vertebral stenotic myelopathy (aka Wobbler Syndrome). One form is called cervical vertebral instability. In this case, ventroflexion of the neck results in spinal cord compression. Most commonly affected sites are C3-4 and C4-5. The other form is known as cervical static stenosis. In this case, the compression is continuous regardless of the neck position. Clinical signs are usually in the form of a wide based stance, conscious proprioceptive deficits, ataxia, paresis, and spasticity which is worse in the hindlimbs. Verminous myelitis results from aberrant migration of parasites through the central nervous system. Clinical signs are very similar to that of EPM. However, EPM occurrence is much more common. Parasites known to undergo aberrant migration in the horse are Strongylus vulgaris, Micronema deletrix, Draschia megastoma, and Setaria spp.

Answer 192

d. An increase in the P-R interval The correct answer is an increase in the P-R interval. First-degree, second-degree, and third-degree blocks are associated with delays in conduction at the level of the atrioventricular conduction system. In a first-degree block, the impulse is still able to transmit through the atrioventricular conduction system; however, it takes longer. Therefore, you will see an increased P-R interval. Second-degree AV block is associated with intermittent AV block in which some but not all P waves are conducted to the ventricles. In third-degree block, there is complete dissociation between the P waves and the QRS complexes. Frequently in third-degree block, the heart rate is slower than normal (20 beats/min) because a subservient pacemaker (i.e. in the AV node or ventricle) has to fire to cause ventricular contraction.

Answer 193

b. This horse most likely has aortic regurgitation due to degeneration of the aortic valve and should have no impacton performance The correct answer is this horse most likely has aortic regurgitation due to degeneration of the aortic valve and should have no impact on performance. Given the location of the murmur and signalment, this should be the logical answer to choose. The thing you need to know is that aortic regurgitation in the horse is usually a degenerative change and there isn't much that can be done about it. Horses are rarely impaired by development of the murmur. In a true pre-purchase exam, you would be wise to recommend a full cardiac work-up to definitively diagnosis the source of the heart murmur. The potential buyer may decline further diagnostics, but at least you will have offered the choice and have provided the proper information to the client.

Answer 194

a. Long term furosemide administration The correct answer is long term furosemide administration. Horses with glomerulonephritis are usually polyuric. Furosemide is only indicated for oliguric renal failure. The other choices are commonly used in the treatment and management of glomerulonephritis. A low protein diet will help decrease the amount of proteinuria and blood urea nitrogen circulating at any given time, therefore helping reduce the degree of azotemia.

Answer 195

c. Calcium carbonate he correct answer is calcium carbonate. Equine urine contains high amounts of calcium carbonate. Magnesium ammonium phosphate (aka struvite crystals) is also occasionally noted in horse urine.

Answer 196

d. Laminitis with rotation of the third phalanx Laminitis, or founder, is severe and has progressed to the point of rotation of the third phalanx. The angle of the hoof wall surface and the dorsal third phalanx are no longer parallel. These radiographic findings along with the clinical signs are diagnostic for laminitis.

Answer 197

b. Neorickettsii risticii, Supportive test - a PCR of blood or feces The correct answer is Neorickettsii risticii, the causative agent of Potomac Horse Fever (PHF). The clues that best indicate PHF are the time of year (disease usually occurs in the summer in the northern states), the high fever and diarrhea, and the presence of laminitis. The horse is also dehydrated and has a profound leucopenia, both consistent with PHF. Salmonella also causes diarrhea and leucopenia, and could be a viable choice, but Salmonella can occur at any time of the year; moreover, laminitis is not as often seen with Salmonella. This question has a practical aspect to it as horses often present with the described history and physical examination findings, and the veterinarian has to decide if he or she wants to treat specifically for PHF; the drug of choice is oxytetracycline. In this clinical situation, you as a veterinarian would have to start treatment empirically as your PCR test will take several days to get results. The good news is that PHF is very susceptible to oxytetracycline.

Answer 198

c. They constantly secrete gastric fluid The correct answer is they constantly secrete gastric fluid. This is unique to equids, as many other species only secrete gastric fluids in response to consumption of food items.

Answer 199

a. Erythromycin Erythromycin is often used in combination with rifampin. Others used are clarithromycin or azithromycin.

Answer 200

a. Inhibition of intestinal motility ## Footnote The correct answer is inhibition of intestinal motility. When xylazine is given at 1.1 mg/kg it decreases the motility of the distal jejunum, cecum, and pelvic flexure for over 2 hours. Xylazine can also transiently decrease cardiac output in a potentially hypovolemic horse with colic. Conversely, xylazine is a potent analgesic and can provide immediate relief to a horse with abdominal pain.

Answer 201

c. Neomycin The correct answer is neomycin. This is followed by gentamicin and then amikacin. Streptomycin is the least nephrotoxic aminoglycoside. Amphotericin B is an anti-fungal and not an aminoglycoside.

Answer 202

a. Epistaxis ## Footnote The correct answer is epistaxis. This occurs due to the fungus eroding the wall of the carotid artery (usually internal carotid).

Answer 203

d. West Nile Encephalitis (WNV); Serum Immunoglobulin M (IgM) capture ELISA The correct answer is WNV. This is a mosquito born flavivirus that affects horses in multiple areas of the United States. Clinical signs are variable and can be mild (muscle fasiculations, slight ataxia) to severe (recumbency). Of note, muscle fasiculations is somewhat characteristic of WNV but fever may be detected in all patients. A readily available diagnostic test is the serum IgM capture ELISA which will detect infection, even in the face of vaccination. There is a vaccine available for WNV, making the clinical presentation less common.

Answer 204

a. Cranial nerves VII and VIII (left side); fracture of the basisphenoid bone The correct answer is damage to cranial nerves VII (facial nerve) and VIII (vestibular nerve) on the left side caused by fracture of the basisphenoid bone. This is a common injury when a fractious young foal rears up and falls backward on the poll. The basisphenoid bone becomes injured resulting in injury to cranial nerves VII and VIII. Damage to the facial nerve results in the muzzle deviation (opposite direction of the side of injury, in this case deviated to the right), ptosis of the left eye and drooping of the left ear. Damage to the vestibular nerve results in the head tilt.

Answer 205

d. Atrioventricular node The correct answer is the atrioventricular node. At the atrioventricular node, we see first-degree AV blocks, second-degree AV blocks, and third-degree AV blocks.

Answer 206

c. Ventricular septal defect The correct answer is ventricular septal defect. There is echo dropout immediately below the aortic valve and extending into the right ventricle. The auscultatory findings also fit with a VSD as the murmur is typically louder on the right. A PDA would cause a continuous heart murmur. There is no narrowing in the LV outflow tract so subaortic stenosis is not evident. There is no evidence of a vegetation or mass on the tricuspid valve so endocarditis is not correct.

Answer 207

a. Granulosa-thecal cell tumor The correct answer is granulosa-thecal cell tumor. The clinical signs and palpation findings are both consistent with this diagnosis. The other choices listed may create a palpable ovarian mass but would not cause atrophy of the contralateral ovary and should not cause infertility.

Answer 208

b. 1.012 The correct answer is 1.012. Isosthenuria would be expected in any horse with chronic renal insufficiency that is causing azotemia. Isosthenuria is typically defined by a urine specific gravity of about 1.008-1.015.

Answer 209

b. Stringhalt Stringhalt is a myoclonic disease affecting one or both pelvic limbs. It causes spasmodic hyperflexion of the leg. The etiology is unknown but sweet pea poisoning is thought to be associated with the condition. Diagnosis is based on clinical signs, but electromyography can be used to confirm the diagnosis. Treatment involves tenectomy of the lateral digital extensor tendon; however, not all cases respond to the treatment. Bog spavin, also known as tarsal hydrarthrosis, is often due to poor conformation and can result in increased synovial fluid formation. Both hindlimbs are usually affected. The horse is usually not lame from this condition. Distension may spontaneously appear and disappear in young horses. Bone spavin is osteoarthritis of the hock. Sweeney is supraspinatous contracture.

Answer 210

a. Anemia ## Footnote The correct answer is anemia. Purpura hemorrhagica is a possible sequela of streptococcus equi infection exposure or vaccination. It develops from a Type III hypersensitivity resulting in immune complex deposition in blood vessel walls and vasculitis. Common clinical signs are as described in the question. This is a nonthrombocytopenic purpura (most horses will have a normal platelet count). Common findings include anemia, hyperproteinemia, hyperfibrinogenemia, hyperglobulinemia, and neutrophilia.

Answer 211

a. Infectious bovine rhinotracheitis The correct answer is infectious bovine rhinotracheitis. There are three subtypes of infectious bovine rhinotracheitis identified. BHV-1.1 (Bovine herpes virus) is responsible for respiratory infections. BHV-1.2 may cause genital infections and respiratory disease. BHV-1.3 (reclassified recently and now called BHV 5) has been known to cause neurologic infections. Since most people are not aware of the reclassification, this aspect of the issue is unlikely to be questioned on a board examination. All of the other listed answer choices can cause the lesion described in the question.

Answer 212

a. Ingestion of moldy feed containing aflatoxins This is a case of photosensitization based on the skin lesions confined to the nonpigmented areas. Primary photosensitization can occur when photodynamic agents are absorbed from the G.I. tract such as Hypericum perforatum (St. John's wort), Fagopyrum esculentum (buckwheat), Ammi majus (bishop's weed), and Cymopterus watsonii (spring parsley). Secondary (hepatogenous) photosensitization occurs when the liver's excretion of phylloerythrin is impaired due to liver damage. Phylloerythrin is derived from the breakdown of chlorophyll by rumen microbes. The best answer in this question is aflatoxins because they are known to cause liver damage. Bracken fern toxicity causes acute hemorrhagic syndrome in cattle. Lupine toxicity primarily causes birth defects. Quercus (oak) toxicity causes GI and renal dysfunction.

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