EQUINE

Question 1

What is string halt?

Answer 1

Stringhalt is a myoclonic disease affecting one or both pelvic limbs. It causes spasmodic hyperflexion of the leg. The etiology is unknown but sweet pea poisoning is thought to be associated with the condition. Diagnosis is based on clinical signs, but electromyography can be used to confirm the diagnosis. Treatment involves tenectomy of the lateral digital extensor tendon; however, not all cases respond to the treatment.

Bog spavin, also known as tarsal hydrarthrosis, is often due to poor conformation and can result in increased synovial fluid formation. Both hindlimbs are usually affected. The horse is usually not lame from this condition. Distension may spontaneously appear and disappear in young horses.

Question 2

What is the problem with treating with piperazine?

Answer 2

The correct answer is large die-off of ascarids resulting in impactions. Treatment with piperazine will result in rapid death of ascarids. If a horse has a large burden of worms, this may be contraindicated as they may die rapidly and result in obstruction, as most likely occurred in this case. There is no reported specific adverse reaction of piperazine in Hanoverian horses. Small bowel bacterial overgrowth is not an issue. This would not happen after treatment with piperazine, especially a day after treatment. Infarction of the caudal mesenteric artery is not seen with use of piperazine.

Question 3

Which of these is the most appropriate treatment for a horse with equine protozoal myeloencephalitis?

Answer 3

The correct answer is trimethoprim-sulfa and pyrimethamine. Equine protozoal myeloencephalitis is caused by Sarcocystis. This combination of drugs blocks folate metabolism by the protozoan at multiple steps and is generally agreed to be the most effective treatment for this condition. Recently, ponazuril has been approved and labeled for the treatment of EPM in horses and works by the same general mechanism.

Question 4

What disease would be a top DDX for equine urinary incontinence?

Answer 4

Cauda equina neuritis and herpes virus myelocephalopathy

Question 5

What are the CS of potomac horse fever?

Answer 5

Colic, fever, laminitis; looks like salmonella

Question 6

What is Fistulous Withers?

Answer 6

Brucella abortus

Question 7

What are the signs of Horner’s in horses?

Answer 7

The correct answer is sweating. Horner’s syndrome is caused by a disruption of the vagosympathetic trunk. Clinical signs include sweating (on the ipsilateral head and neck), enophthalmos (sinking of the eye ball), ptosis (drooping of the eye), and miosis (constricted pupil). Additionally, you will likely see a prolapsed third eyelid due to the enophthalmos allowing the third eyelid to just prolapse.

Question 8

Two mares are presented for crusting dermal lesions on their dorsum and pasterns. The lesions are “paintbrush” like lesions and have purulent material exudating from them. A direct smear of the lesion shows branching, filamentous, gram positive bacteria. What is your most likely diagnosis?

Answer 8

The answer is dermatophilosis. Dermatophilus congolensis is a gram positive, non-acid fast, facultative anaerobic actinomycete. It causes a crusting dermatitis in large animals when there is high moisture on the skin as well as mechanical irritation. Horses with long, wet haircoats are often affected. Lesions are commonly on the dorsum and pasterns of horses and are classically described as paintbrush lesions. It can be diagnosed with a direct smear preparation. Treatment includes keeping the haircoat clean and dry and penicillins if the lesions are severe. Lesions typically heal rapidly.

Question 9

A 4 year old horse presents to you with a mucopurulent nasal discharge, lethargy, and depression. On physical exam, the horse has a temperature of 103.7F (39.8 C) and has markedly enlarged mandibular and retropharyngeal lymph nodes. You suspect that the horse has strangles. What would you expect to see if you aspirated one of the enlarged lymph nodes?

Answer 9

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

Question 10

A 2-year old Quarter Horse presents for intermittent muscle fasciculation followed by weakness. What condition should you suspect?

Answer 10

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.

Question 11

Treatment of stringhalt in a horse involves which of the following?

Answer 11

The correct answer is tenectomy of the lateral digital extensor. Stringhalt is a myoclonic disease affecting one or both pelvic limbs. It causes spasmodic hyperflexion of the leg. The etiology is unknown but sweet pea poisoning is thought to be associated with the condition. Diagnosis is based on clinical signs, but electromyography can be used to confirm the diagnosis. Treatment involves tenectomy of the lateral digital extensor; however, not all cases respond to the treatment.

Question 12

A horse presenting for discharge around the ear should be assessed for this condition.

Answer 12

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

Question 13

How many permanent teeth do horses have?

Answer 13

Horses have between 40-42 permanent teeth.

Question 14

Which of these would you expect to see in a horse that has had significant blood loss?

Answer 14

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

Question 15

You are presented with a 6-month old colt with a 5-day history of lethargy, intermittent diarrhea, weight loss, and ventral edema. A quick check of the PCV and TP reveal a PCV of 30% (28-42%) and TP of 3.2 g/dl (6.8-8.2 g/dl). Abdominal ultrasound (see image) demonstrates thickening of the small intestinal wall. What is the most likely diagnosis based on signalment, history and clinical findings?

Answer 15

Although not as commonly as in pigs, L. intracellularis can infect horses (and other species). Similar to pigs, the infection usually involves weanling age horses and causes thickening of the small intestine and hypoproteinemia. The low protein is commonly observed as ventral edema clinically. Both Clostridium and Salmonella can cause diarrhea at any age but are not as commonly associated with ventral edema. Intussusceptions do occur but also typically result in colic.

Question 16

Which of the following is not believed to be a cause of physitis in young horses?

Answer 16

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

Question 17

Approximately how long does it take for spermatogonia to mature to sperm in the stallion?

Answer 17

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

Question 18

Which cells does caprine arthritis encephalitis virus infect?

Answer 18

monocytes.

Question 19

Where do nephrosplenic entrapments occur in the horse?

Answer 19

The correct answer is between the spleen and the left body wall. The nephrosplenic ligament runs from the left kidney to the spleen, and a nephrosplenic entrapment occurs when a portion of large intestine is looped over the nephrosplenic ligament, becoming trapped between the spleen and the left body wall.

Question 20

What is the most common infectious cause of abortion in horses?

Answer 20

The correct answer is equine herpesvirus. This is the most common cause of late-term abortions and accounts for about 25% of all diagnosed abortions in the horse.

Question 21

A 5-year old brood mare presents with a history of intermittent hind limb lameness. The onset of the lameness has been gradual. The mare is an active cutting horse. With your initial hands-off examination, you compare the structural integrity of both hocks (see image). Without using any further diagnostics, what disease process and corresponding anatomical structures do you suspect is causing the lameness?

Answer 21

The correct answer is bone spavin: osteoarthritis of the distal intertarsal joint and/or tarsometatarsal joint. Bog spavin is synovial distention of the tarsocrural joint, which you cannot see or appreciate with the given image. The only true answer with the information given is osteoarthritis of the distal tarsal and tarsometatarsal joint. All you have to do is memorize which spavin correlates with the appropriate anatomy. This question is designed to help you use the information given and not to get caught up in over analyzing the question.

Question 22

You are examining a 3-year old Thoroughbred gelding for lameness of the right forelimb. The lameness persists with a palmar digital and abaxial sesamoidian nerve block but is improved by 90% after a low 4-point (low palmar) nerve block. The source of the lameness is likely in which region of the limb?

Answer 22

The low 4-point (low palmar) nerve block typically provides local anesthesia to the metacarpophalangeal (fetlock) joint and below. An injury to this area is most likely. The proximal suspensory ligament and carpal-metacarpal joint would require local anesthesia more proximally.An 8-year old Quarterhorse brood mare presents with an acute onset of colic. On presentation she has a heart rate of 58, respiratory rate of 28, and is seen rolling on the ground. CRT is approximately 3.0 seconds and mucous membranes are slightly red. She has rectal temperature is 101.6F (38.7 C). Gastrointestinal sounds are completely absent and gastric reflux yielded 15L of brown- to yellow- colored fluid. Peritoneal fluid analysis yielded a cloudy yellow fluid with a protein of 2.8 gm/dl and white blood cell count of 11,354/ul. Which of the following is not a likely diagnosis?

Question 23

An 8-year old Quarterhorse brood mare presents with an acute onset of colic. On presentation she has a heart rate of 58, respiratory rate of 28, and is seen rolling on the ground. CRT is approximately 3.0 seconds and mucous membranes are slightly red. She has rectal temperature is 101.6F (38.7 C). Gastrointestinal sounds are completely absent and gastric reflux yielded 15L of brown- to yellow- colored fluid. Peritoneal fluid analysis yielded a cloudy yellow fluid with a protein of 2.8 gm/dl and white blood cell count of 11,354/ul. Which of the following is not a likely diagnosis?

Answer 23

The correct answer is strangulating lipoma. The clinical signs are consistent with any of the answer choices. However, a strangulating lipoma is least likely to be the case since this horse is still relatively young. Strangulating lipomas are commonly seen in older horses.

Question 24

What is the signalment for strangulating lipoma?

Answer 24

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.

Question 25

In a horse with bilaterally-prolapsed third eyelids, you should rule out this infection.

Answer 25

The correct answer is tetanus. Other clinical signs may include a sawhorse stance, stiff gait, stiff tail, and sensitivity to auditory and tactile stimuli.

Question 26

A horse is referred to your practice for further evaluation and treatment of glomerulonephritis. Which of the following is not a treatment option?

Answer 26

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

Question 27

What breed of horse is predisposed to the development of cerebellar abiotrophy?

Answer 27

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

Question 28

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?

Answer 28

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.

Question 29

An 8-year old Thoroughbred gelding was presented for acute onset of trembling, excessive recumbency, constant shifting of body weight while standing, and muscle atrophy. The horse is housed in a dry lot with no pasture availability. Diet consists of moderate quality grass hay and sweet feed. The CBC is normal with abnormalities on biochemistry analysis including mild elevation in creatine kinase (CK) and aspartate aminotransferase (AST). Cerebrospinal fluid (CSF) analysis shows no remarkable findings. Based on this information, what disease process do you suspect?

Answer 29

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

Question 30

A 10-month old Arabian presents for persistent superficial and deep digital flexor tendon contracture. What surgical option does this patient have?

Answer 30

The correct answer is distal check desmotomy and proximal check desmotomy. The distal check desmotomy relieves the deep digital flexor contracture while proximal check desmotomy relieves superficial digital flexor contracture. If the contracture is severe, it may recur 2-4 months after surgery. At such time, a suspensory desmotomy is an option but subluxation at the proximal interphalangeal joint is a common consequence.

Question 31

What is the causative agent of malignant edema?

Answer 31

The correct answer is Clostridium septicum. It has been given this name because after inoculation due to some sort of trauma, it will cause pitting edema which infiltrates connective and subcutaneous tissue. Clinical signs are similar to those of Clostridium chauvoei (blackleg), except that there is usually no crepitus. Clostridium novyi type B, Clostridium perfringens type A, and Clostridium sordelli are also known to cause malignant edema.

Question 32

In what situation is an acetylcysteine enema most likely to be used?

Answer 32

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

Question 33

You are examining a 2-year old pony with lameness that worsens after activity or work. The pony displays mild lameness on your exam and is sensitive to deep palpation of the third metacarpal bone of the left front limb. Radiographs reveal periostitis and new bone formation along the second metacarpal bone. No fracture is present. What term describes this condition?

Answer 33

Explanation - This is a description of splints or metacarpal exostosis which involves periostitis of the interosseous ligament between the third and second metacarpal (or metatarsal) bone. Treatment usually involves rest and anti-inflammatory medications, although if the bony exostoses impinge on the suspensory ligament, surgical removal of the proliferative tissue may be indicated.

Sidebone refers to ossification of the alar cartilage of the coffin bone. High ringbone refers to osteoarthritis of the proximal
interphalangeal (pastern) joint. Osselets are inflammation of the periosteum on the dorsal distal epiphyseal surface of the third metacarpal bone and fetlock joint. Thoroughpin is the term for effusion of the tarsal sheath (sheath of the deep digital flexor).

Question 34

The current drug of choice for the treatment of Potomac Horse Fever is _____.

Answer 34

The correct answer is oxytetracycline. Treatment for 7-10 days is usually effective in preventing the progression of the disease.

Question 35

A 1.5-year old Quarter Horse gelding is presented to you for symmetric ataxia, weakness, and spasticity of all limbs, but worse in the hind limbs. When walking, the horse frequently drags his toes and the hind limbs frequently interfere with one another. Based on the signalment, history and physical examination findings, which of the following is the most likely cause of these clinical signs?

Answer 35

The horse in this question has clinical signs most consistent with EDM; cervical vertebral malformation (wobblers) is also a possibility, but was not provided as an answer. The cause of EDM is unknown, but this disease typically affects young horses (< 2-3 years of age; but older horses can develop disease). Clinical signs are a result of diffuse neuronal fiber degeneration of various portions of the central nervous system. This disease has been associated with low serum vitamin E concentrations, suggesting that oxidative damage may play a role in the development of disease.

EMND is typically associated with muscle tremors, shifting of weight while standing, muscle atrophy and recumbency. Botulism is associated with generalized muscle weakness. Cauda equina syndrome causes analgesia of the perineum. EPM can cause a range of clinical signs, but is typically with asymmetric neurologic deficits.

Question 36

This 5 year old Standardbred mare in the picture presents for lameness in the right hind limb. There is a jerking motion as she moves the leg forward. On physical exam, you are able to extend the hock and flex the stifle simultaneously. What is your diagnosis?

Answer 36

The correct answer is peroneus tertius rupture. Damage to the peroneus tertius muscle disrupts the stay apparatus of the hind limb. The characteristic diagnostic feature is the ability to extend the hock and flex the stifle simultaneously because an intact peroneus tertius prevents this.

Question 37

An 8-year old Clydesdale gelding presented to you for a 7 day history of pruritus of the distal limbs, particularly the feathered areas of the leg (see image). Upon further examination, you observe irritation, scabbing, and alopecia of the fetlock region likely due to self-induced trauma secondary to pruritus. The horse is restless and bites at the distal limbs frequently. What is the most likely diagnostic test to lend a diagnosis in this case?

Answer 37

The correct answer is skin scraping to identify the Chorioptes mite on microscopic examination. Chorioptic mange is caused by infestation with Chorioptes equi; this mite typically affects the distal limb region but can also extend to the ventral abdomen. Draft horses are particularly susceptible because of their long feathered hair coat of the distal limbs. Chorioptes is more common in the winter months and causes intense pruritus.

In regard to the other answers, intradermal skin testing is sometimes used to detect insect hypersensitivity, but insect hypersensitivity typically affects the trunk or ventral abdomen. Food allergies are not a major cause of dermatologic diseases in the horse and pemphigus is a generalized disease. Onchocerca can cause pruritus, but is diagnosed via skin biopsy or response to ivermectin therapy.

Question 38

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?

Answer 38

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.

Question 39

A miniature horse presents for colic. What cause of colic are they prone to?

Answer 39

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

Question 40

On a routine screening physical exam, you have noted low serum potassium in a 4-year old Thoroughbred racehorse. Which one of the following is the most likely cause of hypokalemia in a horse?

Answer 40

Loop diuretics cause excessive amounts of potassium to be lost via the urine.

Question 41

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?

Answer 41

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.

Question 42

You are examining a 4-year old horse with a distorted hoof 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?

Answer 42

his 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

Question 43

What is the oldest tooth in the horse?

Answer 43

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

Question 44

A horse presents to you with a laceration across the caudal aspect of the hock; the horse is not weight-bearing, and the hock completely dropped to the ground. What structure has likely been ruptured to cause these clinical signs?

Answer 44

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

Question 45

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?

Answer 45

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.

Question 46

Which of the following is the most plausible reason for finding an elevated serum level of gamma glutamyltransferase (GGT) in a 7-year old horse?

Answer 46

GGT is a marker of hepatobiliary disorders and cholestasis in large animals.

Question 47

An adult horse presents to you for multiple skin lesions. There are patchy areas of erythema, scaling, and alopecia along the ventral midline. There is a diamond-shaped lesion of erythema and scaling along the forehead. According to the owner, the lesions are not pruritic. What is the most likely cause of these lesions?

Answer 47

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

Question 48

A 9-year old Standardbred stallion comes to see you for evaluation of muscle atrophy. You examine the horse and note atrophy of the lateral thigh and gluteal muscles. When the horse is backed up, spasmodic hyperflexion of either hindlimb occurs resulting in a high-stepping gait. Which of the following is most likely responsible for the observed signs?

Answer 48

This case describes a horse with stringhalt or sudden flexion (contraction of the lateral extensor tendons) of one or both hind legs. It is most evident when the horse is backing up slowly or turning. It can involve one or both hind legs. The etiology in some cases is unknown but the condition can be associated with chronic intoxication of sweet peas (Lathyrus spp.). Australian stringhalt has been associated with flatweed ingestion (Hypochoeris radicata). The precise pathogenesis is not understood, but a mycotoxin affecting the long myelinated nerves in the hind limbs has been suggested based on the types of nerve damage seen in affected horses.

Black walnut intoxication is associated with laminitis and colic after exposure to wood shavings of black walnuts. Red maple intoxication is associated with acute hemolytic anemia. Senecio or groundsel intoxication is associated with liver disease after chronic exposure. Castor bean intoxication is associated with severe gastrointestinal irritation and hemorrhagic diarrhea.

Question 49

A 3 month old Arabian colt is presented for 3 episodes of pneumonia; the first episode of pneumonia was observed at 7 weeks of age. Each episode of pneumonia is responsive to oral antimicrobials, but when these are discontinued, evidence of respiratory disease occurs several days later. A complete blood count reveals that the foal is persistently lymphopenic. What condition should you suspect?

Answer 49

The correct answer is combined immunodeficiency. Any Arabian foal with persistent infection should be suspected of having this heritable immunodeficiency of B and T lymphocytes. Typically, foals with CID do not demonstrate evidence of repeated infection until maternal antibodies begin to wane. There is no treatment for this disease.

Question 50

A 4-day old foal presents to you for abdominal distension and depression. The owners describe the foal as having frequent attempts to urinate with only small amounts voided. On physical exam, the foal’s heart rate is 180 beats per minute and respiratory rate is 60 breaths per minute. What is the most likely cause of the foal’s clinical signs?

Answer 50

The correct answer is uroperitoneum. With the foal’s history of pollakiuria combined with abdominal distension, tachycardia, tachypnea, and depression, you should suspect uroperitoneum. The most common cause of uroperitoneum is a ruptured urinary bladder from large amounts of pressure on the urinary bladder that often occurs during parturition. Treatment involves surgical repair.

Question 51

A 3 month old Arabian colt is presented for 3 episodes of pneumonia; the first episode of pneumonia was observed at 7 weeks of age. Each episode of pneumonia is responsive to oral antimicrobials, but when these are discontinued, evidence of respiratory disease occurs several days later. A complete blood count reveals that the foal is persistently lymphopenic. What condition should you suspect?

Answer 51

The correct answer is combined immunodeficiency. Any Arabian foal with persistent infection should be suspected of having this heritable immunodeficiency of B and T lymphocytes. Typically, foals with CID do not demonstrate evidence of repeated infection until maternal antibodies begin to wane. There is no treatment for this disease.

Question 52

What is the most common slab fracture in the horse?

Answer 52

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

Question 53

You are performing endoscopy of the guttural pouch of a 6 year old Quarter Horse gelding presented for dysphagia (see image). What is the most likely causative organism?

Answer 53

Aspergillus is the most commonly identified fungal pathogen in guttural pouch mycosis. While this disease can present with epistaxis, dysphagia is sometimes a presenting complaint. Remember, cranial nerves IX, X, XI, and XII travel through the pouch and may be damaged from mycotic lesions, thus resulting in dysphagia. If you are unfamiliar with endoscopic images of the equine guttural pouch, the mycotic lesion is seen from approximately 1 to 7 o’clock while the stylohyoid bone is evident in the left side of the image.

Question 54

Approximately 80% of all equine ulcers occur on the _______ region of the stomach.

Answer 54

The correct answer is squamous. This is known as the nonglandular region. It is not as able to resist injury from acid as is the glandular region, which is able to secrete mucous and thus protect itself from ulceration.

Question 55

Horses living in a sandy region such as California and Florida tend to be predisposed to developing sand enteropathies. If one is suspected, which of the following treatments will be most effective?

Answer 55

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

Question 56

What are the two common types of ureteroliths and uroliths encountered in the horse?

Answer 56

The correct answer is calcium carbonate and calcium phosphate. Although ureteroliths and uroliths are not terribly common in the horse, these are the stones you would expect to encounter.

Question 57

The treatment of choice for Neorickettsia risticii (Potomac Horse Fever) is what antimicrobial?

Answer 57

Oxytetracycline, given intravenously, is the treatment of choice for horses with Potomac Horse Fever. If this is the cause of the colitis in the patient, response to therapy is typically rapid (improvement noted within 24-48 hours of starting treatment).