Horses II Flashcards
At what age does Galvayne’s groove begin to appear in the horse?
- 5 years
- 15 years
- 9 years
- 6 months
Answer: 9 years
Explanation
The correct answer is 9 years. This is useful for the purposes of aging horses. It is a longitudinal groove noted on I3.
I1 erupts at 2.5 years, I2 erupts at 3.5 years, and I3 at 4.5 years.
The canine tooth erupts at 5 years.
The cup from I1 disappears at 6 years, I2 at 7 years, and I3 at 8 years.
Galvayne’s groove is half way down the tooth at 15 years and then completely down at 20 years of age.
Which of the following fractures in an adult horse has a grave prognosis for return to function?
- P3 (distal phalanx)
- Ulna
- Tibia
- P1 (proximal phalanx)
Answer: Tibia
Explanation
The correct answer is tibia. Fractures of the tibia are usually non-reconstructable comminuted fractures. Due to the lack of soft tissue coverage, these fractures are highly susceptible to infection, which makes them poor candidates for recovery. As long as the articular surface of P3 is not involved, P3 fractures carry a good prognosis. Most P1 fractures are fairly easily repaired with lag screws as long as they are not comminuted. Ulnar fractures are usually treated with bone plates and have a good prognosis, with about 70% of horses returning to function.
A 2-year old Quarter Horse presents for intermittent muscle fasciculation followed by weakness. What condition should you suspect?
- Grass tetany
- Myotonia
- Stringhalt
- Hyperkalemic periodic paralysis
- Tetanus
Answer: Hyperkalemic periodic paralysis
Explanation
The correct answer is hyperkalemic periodic paralysis (HYPP). HYPP is seen in Quarter Horses due to a point mutation in a key part of a skeletal muscle sodium channel subunit. This results in elevation of the resting membrane potential to increase the likelihood of depolarizing. Excess concentrations of potassium can result in failure of the sodium channels to inactivate. Therefore, treatment is directed at decreasing dietary potassium.
***PowerLecture: Musculoskeletal Disorders
Which condition is associated with apical fracture of the proximal sesamoid bones, avulsion fractures of the palmar aspect of the third metacarpal bone, or fractures of the distal third of the small metacarpal bones in horses?
- Suspensory ligament desmitis
- Superficial digital flexor tendonitis
- Sweeney
- Deep digital flexor tendonitis
Answer: Suspensory ligament desmitis
Explanation
The correct answer is suspensory ligament desmitis. The presence of these fractures would indicate ultrasonography as the next diagnostic test to evaluate for suspensory ligament desmitis, since these fractures are present with this condition 25% of the time.
A 9-day old foal is experiencing mild diarrhea. What is the most likely diagnosis?
- Clostridium perfringens
- Lactose intolerance
- Foal heat diarrhea
- Rhodococcus equi
Answer: Foal heat diarrhea
Explanation
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.
***PowerLecture: Foal Diarrhea
A 9-day old foal is experiencing mild diarrhea. What is the most likely diagnosis?
- Clostridium perfringens
- Lactose intolerance
- Foal heat diarrhea
- Rhodococcus equi
Answer: Foal heat diarrhea
Explanation
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.
***PowerLecture: Foal Diarrhea
What is the causative agent of Tyzzer’s disease?
- Clostridium botulinum
- Clostridium perfringens
- Clostridium chauvoei
- Clostridium piliforme
- Clostridium difficile
Answer: Clostridium piliforme
Explanation
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.
The syndrome of right dorsal colitis in horses is associated with which predisposing factor?
- Parasitic damage of the intestinal arteries (i.e. right colic artery)
- Colitis as a result of Salmonella infection
- Administration of beta-lactam antimicrobials at excessive dosages (i.e. Ceftofur)
- Administration of non-steroidal anti-inflammatory drugs (i.e. phenylbutazone)
Answer: Administration of non-steroidal anti-inflammatory drugs (i.e. phenylbutazone)
Explanation
Right dorsal colitis is associated with the administration of NSAIDs. The dose of NSAIDs may be within the normal range or higher than recommended dosages. This disease is also usually associated with more chronic administration of NSAIDs (>1 week). Some horses may be more sensitive to NSAIDs, with clinical signs such as inappetence, intermittent colic, and hypoproteinemia commonly observed.
***PowerLecture: Gastrointestinal Disorders
A mare has aborted due to an equine herpesvirus-1 infection. What would you tell the owner about her future as a breeding horse?
- Future breeding are still possible, and the mare can still produce healthy foals in the future.
- She will be latently infected and should not breed this mare again.
- She should be treated with oral acyclovir for at least 3 weeks to avoid future abortions.
- The mare can maintain a future pregnancy, but the fetus is likely to be born with equine herpesvirus with a low chance of survival.
Answer: Future breeding are still possible, and the mare can still produce healthy foals in the future.
Explanation
The correct answer is future breeding possibilities should be unaffected, but the mare likely has a latent herpesvirus infection. Vaccination of the mare during her next pregnancy against EHV (gestational months 5, 7 and 9) may help lessen the chance of abortion in the future. Acyclovir, while active against herpesvirus is not indicated (and is not well absorbed orally anyway).
A horse presents with urticaria, edema of the extremities, petechiation of the mucous membranes, and a stiff gait. On physical exam, you suspect the horse to have purpura hemorrhagica. Which of these abnormalities is associated with purpura hemorrhagica?
- Anemia
- Prolonged PT and PTT
- Thrombocytopenia
- Hypoproteinemia
Answer: Anemia
Explanation
The correct answer is anemia. Purpura hemorrhagica is a possible sequela of streptococcus equi infection exposure or vaccination. It develops from a Type Ill 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.
A 28 year old Paint stallion presents with an acute onset of colic. On presentation he has a rectal temperature of 99.8F (37.7 C), heart rate of 75 beats/min, respiratory rate of 24 breaths/min, and is pawing and trying to lie down. CRT is approximately 3.0 seconds, and mucous membranes are purple-red. Gastrointestinal sounds are completely absent, and gastric reflux yielded 18L of brown-to yellow-colored fluid. Peritoneal fluid analysis yielded a cloudy yellow fluid with a protein of 3.2 gm/dl and white blood cell count of 11,000/ul. Which of the following is a possible diagnosis?
- Strongylus vulgaris infestation
- Strangulating lipoma
- Right dorsal colon displacement
- Cecal volvulus
- Left dorsal colon displacement
Answer: Strangulating lipoma
Explanation
The correct answer is strangulating lipoma. 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.
This neurologic disease has been associated with a deficiency in vitamin E.
- Cerebellar abiotrophy
- Cervical vertebral stenotic myelopathy
- Equine degenerative myeloencephalopathy
- Dandy-Walker syndrome
Answer: Equine degenerative myeloencephalopathy
Explanation
The correct answer is equine degenerative myeloencephalopathy.
Dandy-Walker syndrome is a rare condition seen in Arabian and Thoroughbred foals which results in a midline defect of the cerebellum and cystic dilation of the fourth ventricle.
The pathogenesis of cerebellar abiotrophy still remains unknown, although genetic, toxic, and infectious causes have all been incriminated.
Cervical vertebral stenotic myelopathy is a developmental disease which is not associated with vitamin E deficiency. The disease results in either continuous or intermittent compression of the spinal cord at the cervical region.
Equine degenerative myeloencephalopathy is the condition recently associated with vitamin E deficiency. 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.
***PowerLecture: Neurologic Disorders
A 5-year old female Quarterhorse has been tentatively diagnosed with duodenitis-proximal jejunitis (DPJ). What other cause of equine colic can DPJ closely resemble?
- Small intestinal obstruction
- Ascarid impaction
- Nephrosplenic entrapment
- Salmonella
Answer: Small intestinal obstruction
Explanation
The correct answer is small intestinal obstruction. Both small intestinal obstruction and duodenitis-proximal jejunitis (DPJ present with similar clinical signs. The problem is that a small intestinal obstruction will be a surgical disease, and duodenitis-proximal jejunitis responds better to medical treatment. The cause of duodenitis-proximal jejunitis remains unknown. Clinical signs include acute colic with increased respiratory rate, heart rate, and pain. Additionally, there will be lots of gastric reflux. After decompression of the stomach via nasogastric intubation and removal of excess gastric/intestinal fluid, horses with DPJ may appear much more comfortable.
***PowerLecture: Gastrointestinal Disorders
A race horse that has been overworked for the past week presents for a stiff gait, lethargy, anorexia, and oliguria. What is the most likely diagnosis?
- Ischemic renal failure
- NSAID toxicity
- Pigment nephropathy
- Pyelonephritis
Answer: Pigment nephropathy
Explanation
The correct answer is pigment nephropathy. Pigment nephropathy occurs as a result of myositis (tying up), which this presentation is consistent with. Nephrosis and subsequent renal failure is caused by large amounts of myoglobin being filtered by the kidney. This usually occurs in horses that have been subjected to extreme conditions such that the animal breaks down a substantial amount of muscle. The same condition can occur with intravascular hemolysis. In this case, the hemoglobin pigment is the culprit. However, this scenario seems to be less common in the horse.
Alpha 2 receptor agonist drugs are routinely used for sedation of horses. Which of the following alpha 2 receptor agonists has the lowest receptor affinity and shortest duration of action?
- Xylazine
- Medetomidine
- Ketamine
- Detomidine
- Romifidine
Answer: Xylazine
Explanation
The correct answer is xylazine. Xylazine has the lowest receptor affinity, duration of action, and has the largest dose requirement of the alpha 2 agonists. Sedative effects of xylazine last for about 20 minutes. Sedative effects of detomidine typically last approximately 90 minutes; however, peak sedation is achieved for 10-20 minutes. Romifidine is similar to detomidine; however, the side effects are supposed to be decreased. Ketamine is a dissociative agent and not an alpha 2 agonist.
Which of these is not an expected lab finding in a horse with pituitary pars intermedia dysfunction (also known as Cushing’s disease)?
- Low urine specific gravity
- Stress leukogram
- Elevated alkaline phosphatase
- Hyperglycemia
Answer: Elevated alkaline phosphatase
Explanation
The correct answer is an elevated alkaline phosphatase. The horse, unlike the dog, does not have a steroid- induced isoenzyme of alkaline phosphatase. Hyperglycemia is common due to the counter-insulin effects of cortisol. Low urine specific gravity is a common feature of Cushing’s seen in dogs and horses and is the reason affected animals are polyuric and polydipsic. The stress leukogram (neutrophilia, lymphopenia) is due to the effects of cortisol as well.
A 2-year old Thoroughbred race horse presents for lameness evaluation. The trainer reports that the lameness has been slowly progressive over the past 3 weeks. You observe the horse walk and see a short, choppy gait in the front legs. There is swelling over the front of both fetlock joints and palpation and flexion of the fetlocks elicits pain. Radiographs show no evidence of new bone formation in the fetlock. You diagnose the horse with osselets (periostitis of the distal dorsal cannon bone). What is the best treatment recommendation?
- Deep digital flexor tenotomy
- Rest, phenylbutazone, and intra-articular injections of sodium hyaluronate
- Palmar digital neurectomy
- Arthrodesis of the fetlock
Answer: Rest, phenylbutazone, and intra-articular injections of sodium hyaluronate
Explanation
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.
***PowerPage: Top 9 Equine Lameness
You are called to a small farm owned by an associate in South America, where you are on vacation with a friend. The associate has a few horses that you were going to ride, but they now have fevers and lesions on the tongue. You notice that a few of his pigs seem lethargic, are not eating, and have snout lesions. You check several and find they are febrile. Based on these findings, you tell your associate that his animals appear to have what disease?
- African horse sickness
- Vesicular stomatitis
- Foot and Mouth Disease
- Encephalomyocarditis virus
- African swine fever
Answer: Vesicular stomatitis
Explanation
Vesicular stomatitis is common in Central and South America and occasionally occurs in the southwestern USA. It is one of the few vesicular diseases that affects both horses and pigs (as well as cattle).
What is the most frequently observed side effect associated with acepromazine use in horses?
- Paraphimosis
- Hypotension
- Seizures
- Arrhythmias
Answer: Hypotension
Explanation
The correct answer is hypotension. 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.
By what mechanism does Parascaris equorum typically cause colic in foals?
- Larval migration
- Intestinal impaction
- Thrombosis of the mesenteric artery
- Immune mediated hypersensitivity
Answer: Intestinal impaction
Explanation
The correct answer is intestinal impaction. In foals, a significant ascarid burden with Parascaris equorum can lead to intestinal impaction and associated colic.
Thrombosis of the mesenteric artery occurs with Strongylus vulgaris infestations.
Immune mediated hypersensitivities may occur in adult horses with Parascaris equorum infestations but is unlikely to be a significant cause of the morbidity seen in foals.
Larval migration can occur with Parascaris equorum but typically will affect the lungs or liver and this stage of the parasite does not lead to colic.
You are asked to evaluate some radiographs of the carpal bones of a newborn foal that may be premature. Upon examination of the radiographs what can you conclude (see picture)?
- The carpal bones are incompletely ossified, suggesting that the foal is premature
- The carpal bones are fully ossified, suggesting a full-term healthy foal
- The carpal bones are partially ossified, which is normal in a full-term healthy foal
- The carpal bones are lytic, suggesting septic arthritis in a newborn foal
Answer: The carpal bones are incompletely ossified, suggesting that the foal is premature
Explanation
The carpal bones are partially ossified in this radiograph. Normal ossification of the cartilage precursors in the carpus occurs in the last part of gestation. Therefore, incomplete ossification suggests that this foal was born prematurely. The carpal bones will ossify as the foal ages, but they can collapse with the weight of the foal placing pressure on the soft cartilage, which may result in misshapen carpal bones and chronic lameness.
A 2-year old Standardbred mare presents for alopecia, erythema, and crusting of the skin around the saddle region. A KOF (potassium hydroxide) preparation shows hyphae and arthroconidia. What is the best treatment option for this horse?
- Excision with wide margins
- Topical anti-fungals
- Oral ketoconazole
- Penicillin
- Cephalexin
Answer: Topical anti-fungals
Explanation
The correct answer is topical anti fungals. The horse in the question has dermatophytosis, or ringworm. Horses are most commonly affected with Trichophyton equinum, T mentagrophytes, and Microsporum gypseum. M canis, M equinum, and T verrucosum are also sometimes the causative agents. The disease typically causes alopecia and crusting around the saddle and girth regions. Diagnosis is made by dermatophyte test media (DTM) or visualization of the fungal elements on KOH preps. Topical azole antifungals are most useful in treating the disease. Systemic antifungals are expensive and have unproven efficacy. Antibiotics such as penicillin and cephalexin are not effective against fungus. Excision of the lesions is not necessary.
You are presented with a 5 year old gelding that stands with his left foreleg in the position shown, with dropped elbow and flexed carpus, fetlock, and digits. When he is walked, he drags the limb and is unable to advance the leg. The horse was placed in left lateral recumbency for a 4 hour surgical procedure to the guttural pouch yesterday. What is the correct diagnosis of his problem?
- Ulnar nerve paralysis
- Equine wobbler syndrome
- Brachial plexus tumor
- High radial nerve paralysis
- Equine dysautonomia
Answer: High radial nerve paralysis
Explanation
The radial nerve is susceptible to damage from pressure when a large animal lays on it without adequate padding and circulation for a prolonged period. The advent of warm water beds for padding this area has greatly decreased the incidence. Rapid and aggressive treatment and excellent nursing care can allow some animals with radial paralysis to recover.
A horse owner in Louisiana calls you frantically concerned that he has heard reports of African Horse Sickness in adjacent states and he wants to know what he can do to protect his horses. Which of the following is the best recommendation for preventing transmission of this disease?
- The owner should not travel to any of the states where the disease is present because the virus is transmitted by fomites and can survive for extended periods
- Institute strict arthropod control measures because the disease is transmitted primarily by Ixodes ticks
- Stable all horses in insect-proof housing, particularly at night because the disease is transmitted primarily by Culicoides flies
- Separate all horses from each other and all other animals because horses are most commonly infected by direct contact with infected animals
- Treat all horses with oxytetracycline because the etiologic agent is exquisitely sensitive to this antibiotic
Answer: Stable all horses in insect-proof housing, particularly at night because the disease is transmitted primarily by Culicoides flies
Explanation
African horse sickness (AHS) is a viral disease of equids that is transmitted by insects, primarily Culicoides.
African horse sickness is endemic in sub-Saharan Africa and outbreaks have periodically extended to the Middle East and southern Spain. The primary and biological vector is Culicoides but the virus may also be transmitted by mosquitoes. The virus has been isolated from certain ticks but arthropod transmission is not believed to play a significant role.
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 forms 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.
Diagnosis can often be made based on history of exposure to endemic areas, clinical signs and lesions but must be confirmed by viral isolation and/or serology. There is no effective treatment and prevention/control can be accomplished by vector control and vaccination. There are multiple serotypes of virus and animals immunized against certain serotypes are still susceptible to others. In an outbreak situation, affected horses should be removed/euthanized and remaining horses should be vaccinated with a polyvalent vaccine until the specific serotype can be determined and then animals should be revaccinated with the corresponding vaccine.
For importing equids from Africa, a 2 month quarantine is required and then horses must test free of virus.
Presence of antibodies does not disqualify a horse from importation. Because of the vector-borne nature of the disease, it is recommended that planes flying from endemic areas be sprayed with insecticides on arrival to disease-free countries.
Two pet horses on a ranch are presented for extreme pruritus at their ventrum. The owners report the pruritus has gotten worse during the summer, and they notice increased numbers of small flying insects around at dusk and dawn. Examination of the horses reveals excoriations, alopecia, and thickening of the skin at the ventrum. One of the flies collected in the field by the owner is a small fly with mottled wings. What is your most likely diagnosis?
- Onchocerciasis
- Tabanus fly bites
- Mosquito hypersensitivity
- Culicoides hypersensitivity
- Chrysops fly bites
Answer: Culicoides hypersensitivity
Explanation
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 dain saling the horting 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 has seasonal variability 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.
One of your clients recently purchased a horse that she plans to add to her stable. She is concerned about potential exposure of the horse to Streptococcus equi subsp. equi. Which of the following is the most sensitive test for detecting carriers of the disease?
- Serology for antibodies to S. equi M protein (SeM)
- Nasopharyngeal culture on Columbia CNA (colistin, nalidixic acid) agar with 5% sheep or horse blood
- PCR of a guttural pouch wash for the S. equi M protein (SeM) gene
- Guttural pouch culture Columbia CNA (colistin, nalidixic acid) agar with 5% sheep or horse blood
Answer: PCR of a guttural pouch wash for the S. equi M protein (SeM) gene
Explanation
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.
A 12-year old Quarter Horse gelding is presented for progressively worsening clinical signs of ataxia, intermittent head pressing and prolonged recumbency over the last month. The heart rate is modestly elevated (HR-48 beats/min) but the temperature and respiratory rate are within normal limits. The CBC and biochemistry profile are relatively unremarkable except for mild elevations in the CK and AST. Based on the suspicion of neurologic disease, you then collect cerebrospinal fluid (CSF) from the lumbosacral space yielding the following results:
CSF fluid analysis:
Total nucleated cell count: 86 cells/microliter (reference interval < 6 cells/microliter)
Protein: 118 mg/dL (reference interval 50-80 mg/dL)
Cytology: 14% neutrophils, 57% lymphocytes, 20% macrophages, 7% eosinophils, and 2% basophils.
Based on the above information, what is the most likely cause?
- Hepatoencephalopathy
- Verminous encephalomyelitis (Halicephalobus deletrix)
- Cervical vertebral malformation (Wobbler syndrome)
- Equine protozoal myeloencephalitis (Sarcocystis neurona)
- Equine herpes myeloencephalopathy (EHV-1)
Answer: Verminous encephalomyelitis (Halicephalobus deletrix)
Explanation
This is a tough question, but the correct answer is verminous encephalomyelitis caused by H. deletrix.
Aberrant migration of helminth or fly larvae through the CNS of horses is uncommon, but is a reported cause of neurologic disease. Causative organisms include Halicephalobus deletrix, Draschia megastoma, Hypoderma, strongyloid nematodes, as well as others. If you did not know the answer immediately, you can deduce the correct answer with knowledge of the other diseases.
Wobbler syndrome is usually observed in younger horses (< 5 year of age) and typically does not cause changes in the CSF.
Equine herpes myeloencephalopathy is a consideration, but clinical signs are typically related to hind-limb paresis, bladder dysfunction, and fecal retention along with a xanthochromic (yellow) CSF from the break-down of RBCs that are associated with the vasculitis induced by the herpes virus.
Hepatoencephalopathy could cause the clinical signs observed here, but no evidence of hepatic failure was presented in the question.
Finally equine protozoal myeloencephalitis (EPM); typically EPM does not cause head-pressing but may be possible. In addition, EPM infection does not typically change the CSF. Therefore, by eliminating these other choices, you are left with verminous encephalomyelitis. Also take note that there is an elevation in eosinophils within the CSF, suggesting a parasitic cause.
A 3-year old Thoroughbred race horse presents for lameness evaluation. The trainer reports that the lameness has been slowly progressive over the past 6 weeks. You observe the horse walk and see a short, choppy gait in the front legs. There is swelling over the front of both fetlock joints and palpation and flexion of the fetlocks elicits pain. Which of the following is the most likely diagnosis?
- Osselets
- Low ringbone
- High ringbone
- Navicular syndrome
- Sidebones
Answer: Osselets
Explanation
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.
Sesamoiditis is usually caused by which of the following in horses?
- Extension of tendonitis
- Penetrating wounds
- Chronic sesamoid fractures
- Septicemia
- Tearing of the ligamentous attachments
Answer: Tearing of the ligamentous attachments
Explanation
The correct answer is tearing of the ligamentous attachments. During strenuous exercise, the insertion of ligaments on sesamoid bones can tear, leading to sesamoiditis. Clinical signs can be similar but are generally less severe than sesamoid fractures (lameness, inflammation). Radiographic findings in sesamoiditis can include new bone formation or osteolytic lesions and radiolucent lines which are prominent vascular channels.
Treatment involves long term rest and NSAIDs. Prognosis is guarded to poor.
You diagnose Pneumocystis carinii pneumonia in a 6-week old Arabian foal. A complete blood count shows:
hematocrit=31% (27-43 %)
neutrophils- 1,300/ul (2,900-8,500/ul)
lymphocytes- 227/ul (1,160-5,100/ul)
monocytes- 800/ul (0-700/ul) eosinophils- 700/ul (0-780/ul)
Which of the following is the most likely reason for this problem?
- Severe combined immunodeficiency
- Exposure to Pneumocystis via infected mosquitoes
- Ingestion of moldy feed
- Aberrant migration of Pneumocystis into the lung
- Failure of passive transfer
Answer: Severe combined immunodeficiency
Explanation
Arabian foals that are homozygous for the SCID gene appear normal at birth but then develop fatal infections, often from unusual organisms like Pneumocystis. The SCID trait is autosomal recessive. A genetic test now exists for this disease.
The owner of a horse farm in the Southeastern United States calls you to come to his place two days after a huge wind storm that knocked down trees and power poles. There are seven ill horses. Upon examination you note lethargy, anorexia, dyspnea, coffee-colored urine, and icterus. Which of the following is the most likely cause?
- Equine infectious anemia
- Babesiosis
- Copper poisoning
- Rattlesnake bite
- Red maple (Acer rubrum) poisoning
Answer: Red maple (Acer rubrum) poisoning
Explanation
Horses seem to eat the leaves when branches are available, and the plant contains an unidentified hemolysin in wilted leaves. Ingestion can be fatal.
Several weeks after sustaining a wound to one of the distal limbs of a horse, the owner brings the animal in for exuberant tissue formation at the site. What is your diagnosis?
- Sarcoid
- Phycomycosis
- Proud flesh
- Squamous cell carcinoma
Answer: Proud flesh
Explanation
The correct answer is proud flesh. Proud flesh is a benign formation of exuberant granulation tissue. Diagnosis of proud flesh is based on history and clinical signs. The key to answering this question is the history of a previous wound at the distal limb. The cause of proud flesh is unknown, but it results in inhibition of epithelialization. Treatment includes excision, skin grafts, irradiation, etc, but all are of questionable efficacy.
In a foal with uroperitoneum, the creatinine in the abdominal fluid will be at least _
_ as much as the serum creatinine.
- 4 times
- 6 times
- One fourth
- Twice
- Half
Answer: Twice
Explanation
The correct answer is twice. This finding is diagnostic for a uroperitoneum. In a foal, this is usually due to urinary bladder rupture at the time of parturition due to large pressures exerted on the urinary bladder during parturition.
***PowerLecture: Foal Uroperitoneum
Treatment of choice for splints (intraosseous desmitis) includes which of the following?
- Local steroid injection
- Arthrodesis
- Antibiotics
- Rest and NSAIDs
Answer: Rest and NSAIDs
Explanation
The correct answer is rest and NSAIDs. Splints or intraosseous desmitis is inflammation of the intraosseous ligament between the 3rd metacarpal (or metatarsal) bone with the small metacarpal (or metatarsal) bones. Periostitis occurs with new bone formation along the splint bones or small metacarpals (or metatarsals) usually due to repetitive concussion, excessive training, poor conformation, or improper shoeing. Radiographs are necessary to distinguish this condition from fractures of the splint bones.
You are called out to a horse farm to look into a disease outbreak. Multiple horses are showing signs of fever, colic, and subcutaneous edema. You find 2 dead horses that do not show rigor mortis with unclotted blood exuding from their noses. Which of these is the LEAST appropriate diagnostic or therapeutic step to take next?
- Look at a blood smear from one of the sick
horses - Administer penicillin to all the febrile horses
- Perform a CBC and Chemistry panel on one of
the sick horses - Perform a field necropsy on one of the dead horses
Answer: Perform a field necropsy on one of the dead horses
Explanation
The answer is perform a field necropsy on one of the dead horses. While many of the signs are non-specific, the unclotted blood and lack of rigor mortis should raise your suspicion that you may be dealing with an anthrax outbreak. Performing a field necropsy would be dangerous to you and to the other horses and people in the area.
A 4 year old Quarter Horse presents to you for progressive neurologic signs of ataxia and paresis. You note asymmetric muscle atrophy of limb musculature. These findings are most consistent with which condition?
- Wobbler syndrome
- Equine protozoal myeloencephalitis
- Equine degenerative myeloencephalopathy
- Cauda equina neuritis
Answer: Equine protozoal myeloencephalitis
Explanation
The correct answer is equine protozoal myeloencephalitis. Equine protozoal
myeloencephalitis (or myelitis) can affect any age horse and is caused by Sarcocystis neurona. It should be suspected in this case due to the asymmetry of clinical signs, as it is a multifocal disease of the central nervous system.
Wobbler syndrome and degenerative myeloencephalopathy are diseases seen primarily in younger horses (< 3-4 years of age).
Degenerative myelopathy causes a symmetrical ataxia.
Cauda equina neuritis typically causes tail rubbing and urinary and fecal incontinence.
Which of the following stallions should definitely not be used for breeding?
- A stallion with a positive bacterial culture from a pre-ejaculate swab
- A stallion with 180 degree rotation of the testicle
- A stallion with previous infection with Taylorella equigenitalis
- A stallion with a previous infection with coital exanthema
Answer: A stallion with previous infection with Taylorella equigenitalis
Explanation
The correct answer is a stallion with a previous infection with Taylorella equigenitalis. This organism is thought to be eradicated in the United States but is the causative agent of contagious equine metritis, which can lead to infertility (there is usually no clinically apparent disease in the stallion). It is okay to breed a stallion with a history of coital exanthema (Equine herpesvirus-3) as long as all lesions are cleared. A 180-degree rotation of the testicle is common and of no clinical significance as is a positive bacterial culture from a pre-ejaculate swab; however, heavy growth of Pseudomonas or Klebsiella may make you think twice, as they can be associated with causing endometritis in mares.
The lesion associated with this horse’s source of colic is pictured below. The lesion causing the pathology seen in the intestine has been separated and is seen to the left of the image. What is the most common signalment for this cause of colic.
- Mid- to older (15-20 years of age) geldings
- Adolescent (3-5 years of age) mares
- Any age stallions
- Horses less than 1 year of age
Answer: Mid- to older (15-20 years of age) geldings
Explanation
You must first identify the cause of colic as being a strangulating lipoma. The lipoma is to the left and has been untangled from the intestine where it was strangulating part of the small intestine (notice the normal colored small intestinal serosa as compared to the dark purple section). There is a strong association with strangulating lipomas occurring in older horses, especially geldings. Thus, mid-to older age geldings is the best answer.
***PowerLecture: Gastrointestinal Disorders
A 3 month old foal presents to you with a cough. On your exam, you note that the horse has a respiratory rate of 50, temperature of 103 F (39.4 C), and has wheezes on auscultation. You also note abdominal tucking on inspiration. You perform a transtracheal wash and find gram positive pleomorphic rods on cytology. What is your diagnosis?
- Streptococcus equi ssp. equi
- Streptococcus equi ssp. zooepidemicus
- Equine influenza
- Rhodococcus (Corynebacterium) equi
Answer: Rhodococcus (Corynebacterium) equi
Explanation
The correct answer is Rhodococcus (Corynebacterium) equi. The signalment and clinical signs are most consistent with Rhodococcus equi infection. The pleomorphic gram positive rods on cytology make this clearly the best choice. The pleomorphic rods of Rhodococcus are often said to look like simplified Chinese characters, so keep this in mind if you are shown cytology on the exam. Another helpful diagnostic tool is the presence of single or multiple abscesses within the lung fields observed via thoracic radiography or ultrasonography.
An 11 year old Quarter Horse mare presents to you for progressive neurologic signs over 4 days. The horse has been vaccinated for rabies only. Signs began with anorexia and depression but moved on to hyperesthesia, propulsive walking and a head tilt. Cerebrospinal fluid analysis shows CSF protein of 75 g/dl with a mononuclear pleocytosis. Which of these is the most likely diagnosis?
- Equine degenerative myelopathy
- Western Equine Encephalitis
- Equine protozoal myeloencephalitis
- Thiamine deficiency
- Wobbler Syndrome
Answer: Western Equine Encephalitis
Explanation
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.
For the PowerPage; Equine Viral Encephalitides
For the PowerLecture: Neurologic Disorders
Clostridioides difficile is a spore-forming bacteria commonly associated with enterocolitis and diarrhea in adult horses and foals. Which of the following statements is NOT correct in regard to C. difficile in horses?
- The 2 main virulence toxins are toxin A and toxin B.
- C. difficile can survive for prolonged periods of time in the spore form.
- Transmission of C. difficile occurs via the oral-fecal route.
- Administration of non-steroidal anti-inflammatory medications. For example flunixin meglumine, is a risk factor for the development of C. difficile enterocolitis.
- C. difficile is a Gram-positive, rod shaped, obligate anaerobe.
Answer: Administration of non-steroidal anti-inflammatory medications. For example flunixin meglumine, is a risk factor for the development of C. difficile enterocolitis.
Explanation
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.
Radiographic abnormalities associated with chronic laminitis in horses include which of the following?
- A distinct lucent line between P3 and the hoof wall on the lateral projection
- Osteophyte formation along the solar margin
- Osteophyte formation between P2 and P3
- A change in the angulation of P3
Answer: **
Explanation
The correct answer is a change in the angulation of P3. Inflammation and degeneration of the lamina can be seen radiographically as rotation of P3 relative to the hoof. Osteophyte formation is not an indication of laminitis. A distinct lucent line is normally seen between the margin of P3 and the hoof on the lateral view of a foot.
***PowerLecture: Laminitis
What breed of horse is predisposed to development of recurrent uveitis and equine night blindness?
- Quarterhorse
- Arabian
- Thoroughbred
- Appaloosa
Answer: Appaloosa
Explanation
The correct answer is Appaloosa. Equine night blindness is a congenital disease that is bilateral and nonprogressive, wherein horses have variable degrees of decreased vision in the dark. Recurrent uveitis is a very important condition in the horse and is actually the most common cause of blindness in the horse.
Appaloosas are overrepresented, but the disease can occur in any breed. It is thought to be related to certain pathogens including Leptospira, Onchocerca, Toxoplasma, Brucella, and other infections, but these relationships are poorly characterized. Affected horses have recurrent bouts of inflammation, and each episode causes progressively worsening intraocular damage. The condition is sometimes referred to as moon blindness.
Which of these statements is most accurate regarding the Coggin’s test for equine infectious anemia?
- It is most effective during an acute episode of anemia
- The test is effective in foals because it detects antigen
- It is effective at diagnosing infection in chronic asymptomatic carriers
- False negatives can occur in foals due to maternal antibody interference
Answer: It is effective at diagnosing infection in chronic asymptomatic carriers
Explanation
The correct answer is it is effective at diagnosing infection in chronic asymptomatic carriers. The Coggin’s test is a test for an antibody; therefore, it carries several drawbacks/limitations. In acute episodes of equine infectious anemia (EIA), there is often not yet adequate production of antibody to detect by this test. In foals, false positives can occur due to acquisition of the antibody in colostrum. Persistently infected horses constitute the majority of cases, and because they are under constant antigenic stimulation, they maintain antibody production and can be very accurately diagnosed with the condition by the Coggin’s test.
Gasterophilus in horses causes which of the following clinical signs?
- Anemia
- Diarrhea
- Gastritis
- Vomiting
- Dermatitis
Answer: Gastritis
Explanation
The correct answer is gastritis. The larvae of Gasterophilus embed themselves in the mucosa of the stomach and can cause a mild gastritis or no clinical signs. The eggs are laid on the hairs of the horse but do not typically cause a dermatitis. They do not develop diarrhea from these infections and horses do not vomit. Anemia does not occur with Gasterophilus infections.
A Paint horse mare gives birth to an all white foal (see image). What clinical sign would you expect to see in a foal with lethal white syndrome?
- Regurgitation
- Constipation
- Anhydrosis
- Ataxia
Answer: Constipation
Explanation
The correct answer is constipation. Lethal white foals have aganglionosis of the intestines which leads to hypomotility, megacolon, constipation, colic, and death.
***PowerLecture: Foal Neuromuscular Disorders
Overo Lethal White Syndrome
Occasionally, all-white (breeding-stock white) foals are produced from Paint horse matings. A small number of these horses have normal gastrointestinal function, but most of these foals are affected by myen-teric aganglionosis and fatal functional intestinal obstruction. This condition is called overo lethal white syndrome (OLWS). Conditions similar to OLWS occur in mice, rats, and humans (Hirschprung dis-ease).
In laboratory animals, these disorders (spot-ting lethal, piebald lethal, and lethal spotting) are characterized by white coat patterning and varying degrees of myenteric aganglionosis. All 3 conditions in rodents and some forms of Hirschprung disease in humans are the result of mutations in either endothelin receptor B (EDNRB) or one of its ligands, endothelin 3.810 The endothelin-signaling pathway is critical for the proper development and migration of neural crest cells that ultimately form melanocytes and enteric neurons. It is now known that substitution of lysine for isoleucine at residue 118 of EDNRB is responsible for OLWS in Paint horses,’ and this mutation has been associated with the parental frame overo phenotype.’’ Most solid-colored horses are homozygous for the Ilel18 allele of EDNRB (wild type), all parents of OLWS foals are het-erozygous, and all OLWS foals are homozygous for the Lys118 allele.
An owner requests that a horse be aged. On oral exam, it is apparent that the canine teeth are beginning to erupt. What is the approximate age of this horse?
- 8 years
- 1 year
- 4 years
- 2 years
- 3 years
Answer: 4 years
Explanation
The correct answer is 4 years. The canine teeth erupt at 4-5 years of age in the horse. It is helpful to remember 2 1/2, 3 1/2, 4 1/2 and then canine. That is…incisors 1, incisors 2, incisors 3, and then the canines will erupt respectively.
A 2-month-old Thoroughbred foal presents with the onset of profuse watery diarrhea and you suspect salmonellosis (see image). There are three specific diagnostic parameters that you, as the clinician, must assess to determine whether or not this patient should be confined to isolation. What are the three diagnostic parameters?
- There are no specific diagnostic parameters for isolation qualification. Any foal or horse with diarrhea should be admitted to isolation.
- Diarrhea, fever, and neutropenia. All 3 of the diagnostic parameters must be present to qualify for isolation.
- Diarrhea, fever, and neutrophilia. All 3 of the diagnostic parameters must be present to qualify for isolation.
- Diarrhea, fever, and neutropenia. Any 2 of the 3 diagnostic parameters qualify for isolation.
- Diarrhea, fever, and neutrophilia. Any 2 of the 3 diagnostic parameters qualify for isolation.
Answer: Diarrhea, fever, and neutropenia. Any 2 of the 3 diagnostic parameters qualify for isolation.
Explanation
The correct answer is diarrhea, fever, and neutropenia. Any 2 of these 3 parameters meet the criteria to admit any equine patient into isolation. 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.
You perform a physical exam on a horse and note pale mucous membranes. A CBC is submitted for analysis. What would you expect to see on your CBC if this horse has hemolytic anemia that has been going on for 10 days or more?
- Macrocytic, normochromic anemia
- Normocytic, normochromic anemia
- Microcytic, hypochromic anemia
- Macrocytic, hypochromic anemia
- Macrocytic, hyperchromic anemia
Answer: Normocytic, normochromic anemia
Explanation
The correct answer is normocytic, normochromic anemia. In the horse, it is very uncommon to see morphologic changes to red blood cells, even if there is a strong regenerative response. Therefore, most types of anemia in the horse will be normocytic, normochromic.
Which of these tests would be the best indicator of moldy sweet clover toxicity in a horse?
- Activated clotting time (ACT)
- Thrombin time (TT)
- Partial thromboplastin time (PTT)
- Prothrombin time (PT)
Answer: Prothrombin time (PT)
Explanation
The correct answer is prothrombin time (PT). Sweet clover can contain a number of fungi that create dicumarol, a warfarin-like toxin. It inhibits vitamin K and interferes with synthesis of factors II, VII, IX, and X.
Because factor VII has the shortest half-life of these factors, it will be depleted first. Factor VII is involved in the extrinsic coagulation pathway and would therefore, be elevated first after ingestion of sweet clover. PT is a measure of the extrinsic pathway (and common). PTT is a measure of the intrinsic pathway (and common).
TT is a measure of the final steps of coagulation taking fibrinogen to fibrin. Cattle are actually affected by moldy sweet clover toxicity more frequently than horses.
A 5-day old foal presents with weakness, rapid breathing, and fever. Which of these methods would be the most useful test for rapid detection of failure of passive transfer?
- Zinc sulfate turbidity test
- Radioimmunodiffusion (RID)
- ELISA (SNAP) test
- Measurement of total protein (refractometer)
Answer: ELISA (SNAP) test
Explanation
The correct answer is the ELISA or SNAP test, which takes approximately 5 minutes to perform. While all the tests listed can be used to evaluate passive transfer, the ELISA would be the most practical and quickest means of evaluation of passive transfer. The RID is the most accurate but takes 24 hours to perform.
Measurement of total protein is a very insensitive test but can be used if no other means are available.
Evaluation of total protein is prone to error because hemoconcentration may falsely elevate the total protein.
***PowerLecture: Failure Of Passive Transfer And Foal Septicemia
You are examining a 12 year old Quarter Horse that was recently in a barn fire (see image). You suspect that the epidermis, dermis and adnexal (i.e. hair, sweat glands) structures are involved. Based on the structures involved, you would classify this as what type of burn?
- 4th degree burn
- 2nd degree burn
- 1st degree burn
- 3rd degree burn
Answer: 3rd degree burn
Explanation
A 3rd degree burn involves the epidermis, dermis, and adnexal structures. Alternatively, a 1st degree (superficial) burn involves the epidermis only; a 2nd degree (partial thickness) burn involves the epidermis and may go down to the deep dermis. 4th degree burns involve total destruction of the skin, fat, fascia, bone and muscle.
This classification scheme would generally apply to all animals, not just horses.
Which of these findings are most consistent with a diagnosis of chronic obstructive pulmonary disease in the horse?
- Early inspiratory wheezes
- End expiratory wheezes
- End inspiratory crackles
- Early expiratory wheezes
- End inspiratory wheezes
Answer: End expiratory wheezes
Explanation
The correct answer is end expiratory wheezes. In chronic obstructive pulmonary disease (COPD), airway diameter is reduced by inflammatory exudate, edema, and bronchoconstriction. As lung volume decreases during expiration, the narrowed bronchioles collapse shut (dynamic airway collapse). This traps air distal to the closure and creates the wheezes heard as the airways narrow towards the end of expiration.
You are examining a 4-year old horse with a distorted hoot in the right front foot. You watch the horse walk and note that the weight of the horse is not distributed uniformly with a focal area on the left side of the heel receiving most of the impact. Closer examination of the hoof reveals that the heel bulb on the left side of the foot is 1 cm higher than the opposite heel when viewed from behind and the coronary band is displaced proximally on the left side. There is flare of the hoof wall on the right side. No hoof cracks or wall separation is present. Which of the following is the name for this condition?
- Sheared heels
- Seedy Toe
- Gonitis
- Club foot
- Scratches
Answer: Sheared heels
Explanation
This is a description of sheared heels which is an asymmetry of the heels that is acquired due to imbalance of the foot resulting in one side of the heel contacting the ground before the other. This creates a shearing force and results in asymmetrical growth. Sheared heels are best treated with repeated corrective trimming of the hoof and application of supportive bar shoes. The prognosis is good when the condition is corrected before additional complications arise.
Seedy toe is characterized by a change in the character of the horn such that the inner surface is crumbly and there may be a cavity due to loss of substance. Scratches is a condition of chronic seborrheic dermatitis of the palmar/plantar aspect of the pastern. Club foot is a condition seen in horses secondary to contracture of the distal interphalangeal joint leading to a steep hoof wall and shortened toe. Gonitis is a term indicating stifle arthritis that is nonspecific to the underlying cause.
Which of these tests would be the best indicator of moldy sweet clover toxicity in a horse?
- Activated clotting time (ACT)
- Prothrombin time (PT)
- Partial thromboplastin time (PTT)
- Thrombin time (TT)
Answer: Prothrombin time (PT)
Explanation
The correct answer is prothrombin time (PT). Sweet clover can contain a number of fungi that create dicumarol, a warfarin-like toxin. It inhibits vitamin K and interferes with synthesis of factors II, VII, IX, and X. Because factor VII has the shortest half-life of these factors, it will be depleted first. Factor VII is involved in the extrinsic coagulation pathway and would therefore, be elevated first after ingestion of sweet clover. PT is a measure of the extrinsic pathway (and common). PTT is a measure of the intrinsic pathway (and common). TT is a measure of the final steps of coagulation taking fibrinogen to fibrin. Cattle are actually affected by moldy sweet clover toxicity more frequently than horses.
You are examining a 3-year old working draft horse on a prepurchase exam. The horse does not show signs of lameness but you note decreased flexibility on palpation of the collateral cartilages of P3 on the right front foot. You take radiographs which show ossification of the collateral cartilages of P3. What should you tell the prospective purchaser?
- This is low ringbone and he should be aware that horses with this condition are at increased risk of developing lameness
- This is splints and in the absence of other signs, it should not affect his decision to purchase the horse
- This is splints and he should be aware that horses with this condition are at increased risk of developing lameness
- This is sidebone and in the absence of other signs, it should not affect his decision to purchase the horse
Answer: This is sidebone and in the absence of other signs, it should not affect his decision to purchase the horse
Explanation
Ossification of the alar cartilage of the coffin bone is known as “sidebone” in horses. Sidebone can be associated with lameness but many horses with sidebone are not lame and horses with sidebone are not thought to be predisposed to developing lameness as a result. Therefore, it is generally believed that in the
lly believed that in the absence of lameness or local sensitivity, sidebone should not affect the purchaser’s opinion of a horse’s soundness. Low ringbone refers to osteoarthritis of the distal interphalangeal (coffin) joint. Splints or interosseous desmitis is inflammation of the interosseous ligament between the 3rd metacarpal (or metatarsal) bone with the small metacarpal (or metatarsal) bones.
An 11-month old Paint gelding is presented to you for symmetric ataxia, weakness, and spasticity of all limbs. When walking, the hind limbs frequently interfere with one another. Based on the signalment, history, and physical examination findings, you suspect equine degenerative myeloencephalopathy (EDM). What diagnostic test would you use to support your suspicion?
- Electromyogram (EMG) demonstrating diffuse increase in motor unit action potentials (MUAP) and positive
sharp waves - No definitive antemortem diagnostic test is available; low serum vitamin E levels are suggestive of EDM
- Collection and analysis of cerebrospinal fluid (CSF) demonstrating increased CS protein and normal CSF nucleated cell count
- Biopsy of the sacrocaudalis dorsalis medialis muscle demonstrating muscle atrophy of type I muscle fibers
- Cervical radiographs and measurement of the saggital ratio
Answer: No definitive antemortem diagnostic test is available; low serum vitamin E levels are suggestive of EDM
Explanation
There is no definitive antemortem test for EDM; it can only be confirmed through histopathologic examination of the spinal cord and brainstem and the identification of diffuse neuronal fiber degeneration of the white matter. However, many cases of EDM have been associated with low serum vitamin E concentrations, so measurement of vitamin E is suggestive of disease. The exact etiology of EDM is unknown, however, oxidative stress and damage to the central nervous system is a prominent theory.
What breed of horse is predisposed to development of recurrent uveitis and equine night blindness?
- Arabian
- Thoroughbred
- Appaloosa
- Quarterhorse
Answer: Appaloosa
Explanation
The correct answer is Appaloosa. Equine night blindness is a congenital disease that is bilateral and nonprogressive, wherein horses have variable degrees of decreased vision in the dark. Recurrent uveitis is a very important condition in the horse and is actually the most common cause of blindness in the horse.
Appaloosas are overrepresented, but the disease can occur in any breed. It is thought to be related to certain pathogens including Leptospira, Onchocerca, Toxoplasma, Brucella, and other infections, but these relationships are poorly characterized. Affected horses have recurrent bouts of inflammation, and each episode causes progressively worsening intraocular damage. The condition is sometimes referred to as moon blindness.
Which 2 antigens are most commonly involved in neonatal isoerythrolysis?
- Qa and Pa
- Aa and Ua
- Aa and Qa
- Pa and Ab
Answer: Aa and Qa
Explanation
The correct answer is Aa and Qa. For whatever reason, these A and Q systems of antigens are highly immunogenic, and almost all cases of neonatal isoerythrolysis are due to incompatibility between these antigen groups. Antigens De, Ua, Pa, and Ab are very rarely associated with causing neonatal isoerythrolysis.
You examine a 6-year old Quarter Horse gelding for a complaint of lameness. He has a short-strided, stilted gait in the forelimbs, is more painful on a hard surface than on a soft grass surface, and head nods when led in a tight circle at the trot in either direction. The hoof tester elicits pain in the posterior third of the foot on both forefeet. The hoof appears normal except that it has narrow heels. A block of the palmar digital nerves seems to result in loss of hoof tester sensitivity and an improved gait. Which of these is the most appropriate treatment?
- A shoe that elevates the toe
- A shoe that elevates the heel
- A shoe that elevates the medial portion of the hoof
- A shoe that elevates the lateral portion of the hoof
Answer: A shoe that elevates the heel
Explanation
The case describes a horse with navicular disease. Pain from navicular disease can be reduced by a shoe that elevates the heel.
Palmar foot pain can be the result of pain from any number of structures including the navicular bone, navicular suspensory or deep digital flexor tendon, navicular bursa, or several other heel areas. Navicular disease is a term used for pain associated with any of these structures.
Acute serum hepatitis in horses, also known as Theiler’s Disease, results in acute clinical signs of lethargy, anorexia, icterus, and hepatoencephalopathy. The diagnosis can be established upon examination of a liver biopsy that would reveal which histopathologic finding(s)?
- Megalocytosis of hepatocytes
- Severe widespread hepatic necrosis
- Severe peri-portal fibrosis
- Marked biliary hyperplasia
Answer: Severe widespread hepatic necrosis
Explanation
The most common microscopic finding is severe hepatocellular necrosis. Inflammatory cells may also be observed. The exact mechanism of disease is unknown but may possibly involve a type Ill hypersensitivity reaction. The original disease was described by Arnold Theiler in South Africa (1918) after vaccination of a herd of horses against African Horse Sickness. Thus, the disease became associated with administration of equine biological products. However, the administration of an equine biological is not always present in the history.
The other answer choices (peri-portal fibrosis, megalocytosis, and biliary hyperplasia) are pathologic hallmarks of pyrrolizidine alkaloid toxicity.
Which of these parasites causes granulomatous skin lesions that often contain small calcified dead larvae inside?
- Onchocerca
- Habronema
- Haematobia
- Culicoides
Answer: Habronema
Explanation
The correct answer is Habronema. 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. 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. 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.
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.
What is the most common gastric neoplasia in the horse?
- Squamous cell carcinoma
- Lymphosarcoma
- Adenocarcinoma
- Mesothelioma
Answer: Squamous cell carcinoma
Explanation
Squamous cell carcinoma is the most commonly reported gastric neoplasia in the horse; the other answers have been rarely observed. Presenting signs include weight loss and colic. Unfortunately, there is no effective treatment at this time.
A one-month old foal develops fever, icterus, and diarrhea acutely. Bloodwork shows hyperfibrinogenemia hypoglycemia, and elevated liver enzymes. Which of these conditions is most likely?
- Herpesviral hepatitis
- Tyzzer’s disease
- Theiler’s disease
- Clostridium novyi type B
Answer: Tyzzer’s disease
Explanation
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.
How long after receiving a puncture wound would you expect to see clinical signs of tetanus if a horse was infected?
- 10-14 days
- 3-5 days
- 1-2 hours
- 3-4 weeks
- 12-24 hours
Answer: 10-14 days
Explanation
The correct answer is 10-14 days. 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.
Carpal fractures in horses occur most commonly in which carpal bones?
- Radial and 3rd carpal bones
- Accessory, 2nd and 3rd carpal bones
- 3rd and 4th carpal bones
- Ulnar and accessory carpal bones
Answer: Radial and 3rd carpal bones
Explanation
The correct answer is radial and 3rd carpal bones. Most carpal fractures in horses occur at the dorsal aspect of the carpal joint, particularly at the radial and 3rd carpal bones. Both chip and slab fractures may occur. These fractures usually result in immediate swelling and severe lameness. Diagnosis is based on radiographs and arthroscopic surgical repair is frequently the treatment of choice.
The owner of an American Paint Horse that is frame overo has bred her horse to a Tobiano horse. The carrier rate for the autosomal recessive disease, ileocolonic aganglionosis (overo lethal white foal syndrome) is 90% in frame overo and 20% in Tobiano horses. Based on these rates, what is the likelihood that the foal born from this mating will be affected by the disorder?
- About 15%
- About 5%
- About 1%
- 50%
- About 25%
- Less than 0.1%
Answer: About 5%
Explanation
You do not need to know anything about the disease in this question in order to get the correct answer. You are told that the disease is recessive.
Because the trait is recessive, homozygotes will be the only individuals affected. In order for a foal to be born homozygous for the trait, BOTH parents MUST be carriers. The chances of both parents being carriers is 90% x 20% (or 0.9 × 0.2) = 0.18 or 18%.
For any autosomal recessive trait, if both parents are carriers, the offspring will have a 25% chance of being homozygous and affected by the disease.
In this example, there is an 18% chance that both parents are heterozygous carriers for the disease.
Applying the 25% rate of passage of both diseased alleles, (0.18 x 0.25) = 0.045, or there is 4.5% chance that the foal will be affected
You perform a physical exam on a horse and note pale mucous membranes. A CBC is submitted for analysis. What would you expect to see on your CBC if this horse has hemolytic anemia that has been going on for 10 days or more?
- Normocytic, normochromic anemia
- Macrocytic, hypochromic anemia
- Microcytic, hypochromic anemia
- Macrocytic, normochromic anemia
- Macrocytic, hyperchromic anemia
Answer: Normocytic, normochromic anemia
Explanation
The correct answer is normocytic, normochromic anemia. In the horse, it is very uncommon to see morphologic changes to red blood cells, even if there is a strong regenerative response. Therefore, most types of anemia in the horse will be normocytic, normochromic.
In what cell of the horse does Anaplasma phagocytophilum survive in?
- Myocyte
- Hepatocyte
- Erythrocyte
- Monocyte
- Neutrophil
Answer: Neutrophil
Explanation
The correct answer is neutrophil. Anaplasma phagocytophilum causes equine granulocytic ehrlichiosis. It can survive in host neutrophils and eosinophils and is can be seen on a blood smear during the acute phase of disease. This in contrast to Neorickettsia risticii, the causative agent of Potomac Horse Fever, which survives in monocytes and is rarely found in a blood smear. Clinical signs of Anaplasma phagocytophilum include depression, limb edema, petechiation, icterus and ataxia and is commonly treated with tetracyclines.
12 L of gastric reflux with a pH of 6.5 in a horse is most indicative of which of the following?
- Gastric ulceration
- Obstruction
- Normal finding
- Colon displacement
Answer: Obstruction
Explanation
The correct answer is obstruction. A pH that is greater than 5 suggests that small intestinal contents are refluxing into the stomach, resulting in an increased pH. Small intestinal ileus is another differential but was not an answer choice.
Which of the following conditions is most likely to cause an elevated level of serum bilirubin in a 7-year old horse?
- Renal failure
- Hemolytic anemia
- Metabolic acidosis
- Acute myopathy
- Hypokalemia
Answer: Hemolytic anemia
Explanation
Hemolysis results in an increase in bilirubin (mainly the unconjugated form) as the damaged red blood cells are removed and the hemoglobin is processed through the liver. Of course, liver disease with failure can also cause elevated bilirubin. In liver disease, both the conjugated and unconjugated forms are elevated.
You are an equine clinician working out in the field. You encounter a colic case and palpate a small intestinal obstruction. You decide to refer the case to a nearby hospital for surgical intervention. What is the most important thing to do before shipping the horse?
- CBC and Chemistry
- Pass a nasogastric tube
- Belly tap
- Abdominal ultrasound
- Sedate
Answer: Pass a nasogastric tube
Explanation
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.
Horses infected with this parasite may be predisposed to thrombosis of the cranial mesenteric artery.
- Strongylus edentatus
- Strongylus equinus
- Trichostrongylus axei
- Strongylus vulgaris
Answer: Strongylus vulgaris
Explanation
The correct answer is Strongylus vulgaris. S. vulgaris undergoes extensive migration after being ingested as an infective larva. They leave the intestinal tract and travel around in the cranial mesenteric artery and its branches. S. equinus and S. edentatus also migrate throughout the body and may be found in the liver, pancreas, and perirenal regions. However, these parasites are not as likely to cause thrombosis of the cranial mesenteric artery.
Trichostrongylus axei is usually only a problem when horses are in pastures with ruminants as this parasite is usually found in ruminants. The larvae of T. axei will penetrate the mucosa and cause ulceration, thickening of the mucosa, and a chronic gastritis. Triodontophorus tenuicollis is a small strongyle and does not migrate outside of the intestines. This particular parasite is known for being able to cause ulceration of the colon.
Which of the following choices correctly identifies the leukocyte in this image of a blood smear from a horse, and the most common types of diseases to which it responds?
A - Neutrophil; wound repair and bacterial infection
B - Lymphocyte; immune disease and viral infection
C - Basophil; allergy and parasitic infestation
D - Monocyte; viral/bacterial infection, and chronic inflammation
E - Macrophage; bacterial and viral infection
Answer: Basophil; allergy and parasitic infestation
This is a basophil, typically associated with allergy or parasite infestation. Basophils (BSO), eosinophils (EOS), and neutrophils (PMNs) are the three types of granulocytic white blood cells.
Phagocytosis is an important function of EOS and PMNs but this is not a primary role of BSOs.
Granulocytic phagocytes have segmented nuclei and cytoplasmic granules - orange/pink in EOS; purple/dark blue in BSOs; pale pink in PMNs.
The granules of basophils contain many mediators of inflammation and large amounts of histamine.
They commonly respond to allergic conditions and parasite infestation, similar to eosinophils.
For more info and images, see the Cornell Clin
Path website:
Hematology Atlas, and Equine blood cells.
Image courtesy of Guy Waterval.
https://eclinpath.com/atlas/hematology/
A 6-year old mare that is 3 weeks post-partum develops abdominal pain and distension acutely. What is the most likely cause?
- Colonic torsion
- Uterine artery rupture
- Small colon impaction
- Uterine torsion
Answer: Colonic torsion
Explanation
The correct answer is colon torsion. It is common in mares that are a few weeks post-partum to have a colonic torsion due to the extra space created in the abdomen after giving birth. When this occurs, it is usually a surgical emergency. Less commonly, colon torsion occurs pre-partum and typically requires surgery as well.
Theiler’s disease is associated with
- Administration of tetanus toxoid
- Horses less than 6 months of age
- Clostridium piliformis
- Administration of tetanus antitoxin (or other equine biological products such as equine plasma)
Answer: Administration of tetanus antitoxin (or other equine biological products such as equine plasma)
Explanation
The correct answer is administration of tetanus antitoxin.
For the PowerPage™ on this topic, view Hepatobiliary Diseases of Horses For the PowerLecture on this topic, view
• Hepatobiliary Disorders (4:57).
Theiler’s disease is associated with
- Administration of tetanus toxoid
- Horses less than 6 months of age
- Clostridium piliformis
- Administration of tetanus antitoxin (or other equine biological products such as equine plasma)
Answer: Administration of tetanus antitoxin (or other equine biological products such as equine plasma)
Explanation
The correct answer is administration of tetanus antitoxin.
For the PowerPage™ on this topic, view Hepatobiliary Diseases of Horses For the PowerLecture on this topic, view
• Hepatobiliary Disorders (4:57).
Which of these nerve blocks is used to examine the eyes of a horse?
- Corneal nerve block
- Oculomotor nerve block
- Trigeminal nerve block
- Auriculopalpebral nerve block
Answer: Auriculopalpebral nerve block
Explanation
The correct answer is auriculopalpebral nerve block. Blocking this branch of cranial nerve VII (facial nerve) disrupts the motor innervation to the orbicularis oculi, which is the muscle that closes the eye. In the horse, this muscle is very strong and can prevent a thorough ocular exam.
To perform this block, lidocaine is injected subcutaneously at the caudal aspect of the zygomatic arch where the nerve is palpable. Because this is a motor nerve, the eye will not be able to close as well, but there is no anesthesia of the tissue.
What is true about regurgitation in horses with colic?
- Occurs secondary to cecal impactions more
often than small intestinal obstructions - Usually means a guarded to poor prognosis
- Never associated with gastric rupture
- Is seen commonly
Answer: Usually means a guarded to poor prognosis
Explanation
The correct answer is usually means a guarded to poor prognosis.
Horses have an extremely tight lower esophageal sphincter tone and regurgitation will only occur when a very great pressure is exceeded. When this pressure is exceeded, there may be other damage such as gastric rupture.
High pressure build up can occur with small intestinal obstructions. Cecal impactions are farther downstream and less likely to result in regurgitation.
What is the most common form of neoplasia seen in the intestines of a horse?
- Leiomyosarcoma
- Squamous cell carcinoma
- Lymphosarcoma
- Lipoma
Answer: Lymphosarcoma
Explanation
The correct answer is lymphosarcoma. 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.
Which of the following is not a common cause of dysphagia in the horse?
- Snake bite
- Bristle grass
- Trauma
- Actinobails lignieresi
- Streptococcus equi
Answer: Actinobacillus lingerensi
Explanation
The correct answer is Actinobacillus lignieresii. This is mainly a problem in ruminants (woody tongue).
A 5-month old Thoroughbred filly is presented to you with enlargement of the right tarsocrural joint of 5 days duration. Upon examination, the filly has a very subtle lameness of the right hind limb and there is diffuse swelling of the joint. The filly appears otherwise alert and healthy. Sterile collection of synovial fluid from the affected joint reveals the following results:
Total Protein- 3.0 gm/dL
Total nucleated cell count- 760 cells/mcL
Cytology- 85% mononuclear cells, 15% neutrophils
After reviewing the synovial fluid analysis, you perform a series of radiographs on the tarsocrural joint (see image).
What is the most likely diagnosis in this filly, based on the clinical signs, synovial fluid analysis, and radiographic findings?
- Osteochondritis Dissecans (OCD) of the lateral trochlear ridge of the right talus
- Mild collapse of the right central tarsal bone as
a result of incomplete ossification of the tarsal bones - Lysis of the trochlear ridge of the right talus
from chronic septic arthritis - Physitis of the right distal tibial growth plate
Answer: Osteochondritis Dissecans (OCD) of the lateral trochlear ridge of the right talus
Explanation
The correct answer is OCD of the lateral trochlear ridge. Horses with OCD are typically presented for veterinary examination between the ages of 4 months to 2 years of age with clinical signs of effusion and/or lameness. However, lameness is not always evident.
Analysis of the synovial fluid can be normal or demonstrate evidence of mild inflammation. Normal synovial fluid analysis values are: Total Protein < 2.5 gm/dL, Total Nucleated Cell Count < 500 cells/mcL, Cytology primarily (> 90%) mononuclear cells.
In regard to the other possible answers, incomplete ossification of the tarsal bones can occur and result in crushing of the small tarsal bones; however, radiographs in this case do not support this finding. As well, septic arthritis can cause lysis of bone, but the patient is typically very lame and has evidence of severe inflammation within the joint (i.e. > 20,000 cells/mcL in synovial fluid).
A 2-year-old Quarter horse filly presents with a history of intense pruritis and alopecia in the perineal area (see image). The owners indicated that they noticed the filly rubbing her tail head and perineal area along fences for a period of one week. What diagnostic test will you use to confirm your top differential?
- A fecal flotation to confirm Oxyruis equi
- A scotch tape test to confirm Oxyuris equi
- A scotch tape test to confirm Strongyloides vulgaris
- A superficial skin scrape to confirm Chorioptes spp.
- A fecal flotation to confirm Cyathostomiasis
Answer: A scotch tape test to confirm Oxyuris equi
Explanation
The correct answer is a scotch tape test to confirm Oxyuris equi, the equine pinworm. 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.
Oxyuris equi in Horses
Equine pinworms are commonly found worldwide. There are two species: Oxyuris equi and Probstmayria vivipara. However, P vivipara has not been found to be clinically relevant and is not discussed further.
The infective stage of O equi is the embryonated egg. Upon ingestion by a horse, L3 larvae are released and invade mucosal walls, primarily in the ventral colon and, to a lesser extent, the cecum. They enter the intestinal lumen as L4 larvae and move to the dorsal colon, which is the predilection site for the adult stage. Gravid females migrate through the descending colon and rectum to deposit their eggs in packets onto perianal skin (8,000-60,000 eggs in one deposit) and then die in the environment.
Infection by O equi can occur in horses of any age and takes approximately 5 months to complete. Adult females can sometimes be observed in the horse’s feces and, because of their stout appearance (length 5-10 cm), can be mistaken for ascarids. However, their tapered posterior ends can confirm identification.
Clinical Findings:
Although O equi larval stages cause inflammatory reactions in the mucosal walls of the cecum and ventral colon, associated clinical signs have not been described. Egg masses can produce local perianal irritation and pruritus that can progress to tail rubbing. Yellow or brown egg masses can sometimes be observed in the perianal area. Clinical laboratory findings are typically unremarkable.
Diagnosis
• Microscopy to identify O equi eggs collected from perianal skin
• Observation of adult females in feces
In cases of O equi infection, direct microscopy of egg mass material from the perianal area reveals numerous eggs, which are morphologically distinguishable from other equine helminth egg types (see O equi egg image).
A sample of 0 equi eggs can be collected by pressing the sticky side of a piece of cellophane tape onto the perianal skin and then applying the tape to a glass slide for microscopy. Alternatively, a lubricated tongue depressor can be used to gently scrape the skin surface for subsequent microscopy.
Fecal flotation and egg counts are not useful in diagnosing O equi infection, because the eggs are generally not released into feces. Female worms can sometimes be observed protruding from the anus as they deposit eggs or can be found in feces or attached to rectal sleeves after rectal examination.
Because tail rubbing can be due to multiple factors, differential diagnoses for this behavior should be considered.
Treatment
• Benzimidazoles
• Supportive care
Ivermectin and moxidectin should not be expected to work against O equi, because there are reports of resistance to this drug class. Benzimidazoles (fenbendazole [5 mg/kg, PO, once] or oxibendazole [10 mg/kg, PO, once]) are effective anthelmintics. Pyrantel efficacy against O equi varies.
Attempts to administer anthelmintics via rectal lavage are not useful, given that O equi adult females are only transiently found in the rectum and their predilection site is the dorsal colon.
Supportive care for O equi infection consists of thorough washing of the perianal area and treatment of skin lesions, as appropriate.
Prevention
Little is known about measures that effectively prevent O equi infection. However, stable and stall hygiene could be considered, because eggs can be deposited onto various objects as a result of tail rubbing.
Zoonotic Risk
O equi poses no zoonotic risk.
Gastrointestinal Parasites of Minor Clinical Importance in Horses
This 2 year old mare in the picture presents for an intermittent left thoracic limb lameness which resolves after working the horse. On physical exam, a palmar metacarpal bulge, heat and tenderness is detected upon palpation. What is your diagnosis?
- Tendonitis
- Subsolar abscess
- Laminitis
- Suspensory ligament desmitis
Answer: Tendonitis
Explanation
The correct answer is tendonitis. The intermittent lameness and bulge at the metacarpals are classic for bowed tendon or tendonitis.
***PowerPage: Top 9 Equine Lameness
Tendonitis and Desmitis
Most commonly affected tendons causing lameness are suspensory ligament especially proximally), deep digital flexor tendon, and superficial digital flexor tendon.
Pathogenesis: acute trauma or chronic weakening of over use.
DSLD = Degenerative Suspensory Ligament Desmitis/Disease:
- Not an athletic overuse injury but a progressive failure of collagen fiber repair in the suspensory ligament apparatus.
- Gradual enlargement but weakening of suspensory ligament leads to a significant fetlock drop, also positive to flexion, often bilateral or all legs.
- Most common in Peruvian Paso Finos but recognized in most breeds.
Clinical Signs:
- Swollen tendon or tendon sheath, painful to palpation
- Mild to moderate lameness at a trot.
- Severe tears may be lame at the walk but almost always weight bearing.
Diagnosis: clinical signs and ultrasonography. Tears within hoof capsule or more subtle injuries may require MRI to diagnose.
- Ultrasonography: focal anechoic lesions in acute lesions; chronic abnormal fiber patterns.
- Radiography: secondary ossification at sites of attachment to bone in chronic lesions.
Treatment:
- Initial rest followed by long rehabilitation program (6-12 months).
- Fasciotomy, neurectomy.
- Additional therapies to speed healing such as platelet-rich plasma injection (PRP), shockwave therapy, etc.
In June, you are asked to examine an 8 year old horse which has been out in a California pasture for over a month. The horse is thin and mildly depressed. There is a tremor of the lips and tongue, and when feed is offered, the lips are pulled back indicating marked dystonia of the facial muscles. The horse is unable to prehend the feed. Which of the following causes should you look for to match these clinical signs?
- Aberrant strongyle migration
- Ethylene glycol
- Lead
- Sarcocystis
- Yellow star thistle
Answer: Yellow star thistle
Explanation
Yellow star thistle is Centaurea solstitialis. In some horses which ingest large quantities, it can cause nigropallidal encephalomalacia, which is loss of the globus pallidus and substantia nigra, and extrapyramidal nuclei, which control muscles of prehension. Loss of these nuclei causes tremors and dystonia of the lip muscles and tongue.
Centaurea repens (Russian knapweed) can also cause similar lesions.
How many pairs of ribs does the normal horse have?
- 21
- 10
- 18
- 13
Answer: 18
Explanation
The correct answer is 18. The horse has 18 pairs of ribs.
A 23 year old horse is most likely to have what type of valvular regurgitation?
- Mitral regurgitation
- Pulmonic regurgitation
- Aortic regurgitation
- Tricuspid regurgitation
Answer: Aortic regurgitation
Explanation
The correct answer is aortic regurgitation. Degeneration of the aortic valve is the most common reason for aortic regurgitation and is present in a lot of older horses as an incidental finding.
On auscultation you will hear a holodiastolic murmur with a point of maximum intensity over the aortic valve area.
A uterine biopsy is most useful for which of the following in a mare?
- Predicting if a mare can undergo parturition without dystocia
- Predicting if a mare can become pregnant
- Predicting where a mare is in the estrus cycle
- Predicting if a mare can carry a foal to term
Answer: Predicting if a mare can carry a foal to term
Explanation
The correct answer is predicting if a mare can carry a foal to term.
Uterine biopsies in horses are most commonly used to determine the amount of fibrosis present in an older mare’s uterus, which indicates her ability to carry a foal to term.
Biopsies can be categorized into Kenney categories, which is a scoring system from 1-3
where a “1” means there are minimal changes and a “3” indicates marked changes.
A mare with a score of “3” has approximately a 5% chance of carrying a pregnancy to term. However, she may still be able to get pregnant.
Biopsy will show some changes that reflect the phase of the cycle, but is not an accurate way to determine a mare’s current phase.
A 3-year old steeplechaser horse presents to you for lameness. The owner reports that the horse developed a short-striding lameness of the left pelvic limb after an event and that the horse is reluctant to bear full weight on the left hind leg. On examination, you notice a prominent bump to the left of midline on the topline of the hindquarters (croup). What is the most likely diagnosis?
- Gonitis
- Ruptured peroneus tertius
- Stringhalt
- Sacroiliac luxation
- Upward fixation of the patella
Answer: Sacroiliac luxation
Explanation
This case describes the common clinical findings in sacroiliac luxation/subluxation in horses.
Jumping horses are commonly affected. The short strided gait is consistent with but not specific for this condition. The raised croup differentiates sacroiliac luxation from some other options in this case.
Upward fixation of the patella is not a traumatic condition as you should suspect based on the history here. It does cause a short strided gait and toe-dragging. The tell-tale sign of this condition is a hind limb in rigid extension that is unable to flex.
Gonitis is a term indicating stifle arthritis that is nonspecific to the underlying cause.
Stringhalt is involuntary flexion of the hind limb and is usually bilateral. Stringhalt is treated with lateral digital extensor tenectomy.
A ruptured peroneus tertius is characterized by the ability to simultaneously extend the hock and flex the stifle.
Gonitis and Osteoarthritis in Horses
Merck
Mild to moderate inflammation of the femorotibial and femoropatellar joints of unknown origin is common. Severity of lameness varies. Synovitis and capsulitis may result from athletic sprain of the joints. Mild trauma to the articular cartilage, menisci, or any of the ligaments of the stifle may produce mild to moderate synovitis. Mild synovitis usually responds to rest and intra-articular and systemic anti-inflammatory drugs.
If joint inflammation and lameness persist, further diagnostic investigation and arthroscopic examination are advisable to assess concurrent or causative injuries and to prevent ongoing degenerative joint disease and development of osteoarthritis.
Osteoarthritis of the femorotibial or femoropatellar joints may follow any of the causes of stifle lameness described and usually results in persistent lameness of varying severity. Diagnosis is confirmed with intra-articular anesthesia and radiography. Radiographic changes include periarticular remodeling with osteophyte formation and remodeling of the joint margins (particularly the medial tibial plateau), changes in the subchondral bone, narrowing of the joint space, and dystrophic mineralization of the soft tissues.
The prognosis for athletic soundness in horses with osteoarthritis of the stifle is poor, and treatment is usually palliative. Newer techniques for arthroscopy and regenerative therapy may offer some hope for severely affected joints.
Rupture of the Fibularis (Peroneus) Tertius in Horses
Merck
The fibularis (peroneus) tertius is a tendinous structure that originates from the extensor fossa of the femur and runs over the craniolateral aspect of the tibia to insert on the dorsoproximal aspect of the third metatarsal bone, the calcaneus, and the third and fourth tarsal bones. It is part of the reciprocal apparatus of the hindlimb, which means there is concurrent flexion and extension of the hock and stifle. Rupture of the fibularis tertius may occur as a result of hyperextension of the limb and usually occurs in the middle of the crus, or laceration may occur on the dorsal aspect of the tarsus. Avulsion of the origin on the fibularis tertius is rare in mature horses but may occur in young animals.
Clinical signs are pathognomonic, because rupture of the fibularis tertius means horses are able to extend the hock while the stifle is flexed. Horses are able to bear weight on the affected limb. At walk, the gastrocnemius and superficial digital flexor muscles appear rather flaccid, and there is a characteristic dimple on the caudodistal aspect of the soft tissues of the crus. At trot, an obvious lameness is usually evident, with delayed protraction of the limb due to overextension of the hock.
Diagnosis is usually based on clinical signs and can be confirmed with ultrasonography.
Conservative treatment with 3-4 mo of stall rest followed by slow and careful reintroduction to exercise usually results in complete resolution of signs and return to athletic soundness.
Stringhalt
Merck
Stringhalt is a gait abnormality characterized by exaggerated upward flexion of the hindlimb that occurs at every stride at walk. The gait abnormality usually lessens at trot and is not evident at canter. It may occur unilaterally or bilaterally. All degrees of hyperflexion are seen, from mild, spasmodic lifting and grounding of the foot, to extreme cases in which the foot is drawn sharply up until it touches the belly and is then struck violently on the ground. In severe cases, there is atrophy of the lateral thigh muscles. In Australian stringhalt and lathyrism, the condition may be progressive and the gait abnormality may become so severe that euthanasia is warranted. Mild stringhalt may be intermittent. The signs are most obvious when the horse is sharply turned or backed. In some cases, the condition is seen only on the first few steps after moving the horse. The signs are often less intense or even absent during warmer weather. Although it is regarded as unsoundness, stringhalt may not materially hinder the horse’s ability to work, except in severe cases when the constant concussion gives rise to secondary complications. However, the condition may make the horse unsuitable for some equestrian disciplines (eg, dressage).
The etiology is unknown, but lesions of a peripheral neuropathy have been identified in the sciatic, peroneal, and tibial nerves. Severe forms of the condition have been attributed to lathyrism (sweet pea poisoning) in the USA and possibly to flat weed intoxication in Australia.
Diagnosis is based on clinical signs but can be confirmed by electromyography. If the diagnosis is in doubt, the horse should be observed as it is backed out of the stall after hard work for 1-2 days. False stringhalt sometimes appears as a result of some temporary irritation to the lower pastern area or even a painful lesion in the foot.
When intoxication is suspected, removal to another paddock may be all that is required. Many of these cases apparently recover spontaneously. In chronic cases, tenectomy of the lateral extensor of the digit, including removal of a portion of the muscle, has given best results. Improvement may not be evident until 2-3 wk after surgery, and not all cases respond. This is not surprising, because the condition is a distal axonopathy. Other methods of treatment include large doses of thiamine and phenytoin.
How is equine viral arteritis transmitted?
- Mosquito
- Transplacentally
- Tick
- Venereally
Answer: Venereally
Explanation
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.
Comprehensive Information on Equine Viral Arteritis
- Definitions:• Equine Viral Arteritis (EVA): A contagious viral disease of equids caused by Equine Arteritis Virus (EAV).
- Causative Agents:• Equine Arteritis Virus (EAV): A small, enveloped, positive-sense, single-stranded RNA virus of the family Arteriviridae.
- Pathophysiology:• Transmission: Direct contact with respiratory secretions, venereal transmission, and indirectly via fomites.
• Infection Mechanism: EAV infects macrophages and endothelial cells, causing widespread vasculitis. It can also cause abortion by infecting the placenta. - Clinical Signs:• Respiratory: Fever, nasal discharge, conjunctivitis, and limb edema.
• Reproductive: Abortions, usually in the late stages of pregnancy.
• Neurologic: Ataxia and encephalitis in severe cases.
• Other: Swelling of the limbs and prepuce, subfertility in stallions. - Diagnosis:• Laboratory Tests: Virus isolation, RT-PCR, serology, and immunohistochemistry.
• Sample Collection: Nasopharyngeal swabs, blood, and tissues from aborted fetuses. - Treatment:• Supportive Care: Antipyretics, anti-inflammatory drugs, and diuretics.
• Symptomatic Treatment: Reduces fever and swelling. - Prevention and Control:• Vaccination: Modified-live vaccines in North America and inactivated vaccines in Europe.
• Biosecurity Measures: Isolation of infected animals, disinfection of equipment, and management of breeding programs. - Medications:• NSAIDs: Used for reducing fever and inflammation.
• Examples: Flunixin meglumine.
• Diuretics: To manage edema.
• Examples: Furosemide.
Summary of Relevant Information:
• Causative Agents: Equine Arteritis Virus (EAV). • Symptoms: Fever, nasal discharge, conjunctivitis, limb edema, abortions. • Clinical Changes: Vasculitis, endothelial damage, placental infection. • Assessment: Virus isolation, RT-PCR, serology. • Treatment: Supportive care, antipyretics, diuretics. • Medications: NSAIDs, diuretics.
For detailed information, visit the Merck Veterinary Manual on Equine Viral Arteritis.
What stimulates antidiuretic hormone (ADH) secretion in the horse?
- Hypoosmolality and increased circulating volume
- Hyperosmolality and decreased circulating blood volume
- Hyperosmolality and increased circulating blood volume
- Hypoosmolality and decreased circulating volume
Answer: Hyperosmolality and decreased circulating blood volume
Explanation
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.
A 26-year old horse presents for evaluation of increased thirst and urination. On exam, you note that the pony has a long curly hair coat and you question the owner who reports that this hair coat has developed gradually over the past 6-9 months. Which of the following diagnostic tests would be most useful in confirming the most likely diagnosis?
- Water deprivation test
- Plasma ACTH concentration
- Serum total and free T4 levels
- Trypsin-like immunoreactivity
- Blood glucose curve
Answer: Plasma ACTH concentration
Explanation
The correct answer is plasma ACTH concentrations as 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 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. However, measurement of plasma ACTH concentrations is a simple and acceptable test (must be compared to seasonal reference intervals as the concentration of ACTH fluctuates during the year). Horses with PPID will have elevated plasma ACTH concentrations. The thyrotropin-releasing hormone (TRH) stimulation test has also been suggested as a test for PPID and causes a significantly higher concentration of ACTH in PPID horses. However, TRH is may not be readily available.
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.
A newborn foal has seizures that, based on history, you believe may be the result of asphyxia associated with difficult parturition. At present the foal is breathing well, the airways are clear, the rib cage is moving appropriately, and the mucous membranes are pink. Which of the drugs listed would be most appropriate to use in the foal at this time to help control seizures?
- Furosemide
- Dopamine
- Diazepam
- Caffeine
- Metoclopramide
Answer: Diazepam
Explanation
Diazepam is a safe anticonvulsant (benzodiazepine) that will not significantly impair respiration at the normal dose.
You are called out to a barn to perform a pre-purchase exam on a 5-year-old Thoroughbred gelding that is to be used for eventing. You notice no abnormalities on physical exam, until you auscult the heart. As you listen, you detect an occasional dropped heartbeat that seems regularly irregular. You continue with your exam, which includes observing the horse at a walk, trot, and canter. You auscult the heart again after exercise. At that time, the rhythm is normal. What do you tell the potential buyer?
- This is a potentially significant arrhythmia and an ECG is recommended prior to purchase
- This horse has a significant arrhythmia that makes the horse unsuitable for eventing
- This is a common incidental finding in horses and not a cause for concern
- This is a potentially significant arrhythmia and a Doppler ultrasound is recommended prior to purchase
Answer: This is a common incidental finding in horses and not a cause for concern
Explanation
2nd degree AV block is a common incidental finding in horses at rest, caused by high vagal tone. It typically resolves with exercise, as it did in this case.
If the arrhythmia is not detected post-exercise, this incidental finding will not decrease the horse’s athletic potential.
If the arrhythmia persisted after exercise, further diagnostics such as ECG and Doppler ultrasound would be indicated.
