1
Q
Which is the most common congenital cardiac defect in horses?
A
Ventricular septal defect
2
Q
What is the most common cause of viral diarrhea in foals?
A
Rotavirus
(same in calves)
3
Q
What is the most common skin tumor of horses?
A
Equine sarcoid
4
Q
In the mare, the embryo is mobile during early pregnancy. The embryo becomes fixed (implanted) by day:
- A. 16-17
- B. 12-14
- C. 8-10
- D. 5-7
A
A. 16-17
5
Q
Which body systems are affected in horses with white snakeroot poisoning?
A
Mainly skeletal and cardiac muscle
This explains the muscle tremors, weakness, choke, and cardiac arrhythmias observed clinically.
6
Q
Which telltale medication history often precedes the diagnosis of right dorsal colitis in horses?
A
Nonsteroidal anti-inflammatory drugs
(NSAIDs, especially phenylbutazone)
7
Q
What is a common cause of ataxia and proprioceptive deficits in horses that can be found worldwide?
A
Cervical vertebral stenotic myelopathy
(wobbler syndrome)
8
Q
If maxillary sinus trephination in a horse exceeds the dorsal boundary for this procedure, which important structure can be lacerated?
A
The nasolacrimal duct
(within the infraorbital canal)
9
Q
What is the clinical manifestation of horses infected with Brucella abortus?
A
“Poll evil” or “fistulous withers”
Fistulous tracts originating from the atlantal or supraspinous bursae, respectively.
10
Q
You choose to sedate a stallion prior to floating its teeth, but unwisely you choose acepromazine as part of your sedation protocol. Which specific complication might occur in this patient that does not occur in other species?
A
Paraphimosis
(uncommon but reported)
The protrusion of the penis may last for extended periods of time (e.g., >2 hours).
11
Q
What is the long-term prognosis for an Arabian foal with juvenile idiopathic epilepsy: good, guarded, or poor?
A
Good
(use protective gear and anticonvulsant therapy then wean off)
Cessation of seizures usually occurs by 1 year of age.
12
Q
You examine a pregnant mare at 15 days’ gestation and identify twins; you manually crush one via rectal palpation.
What are two reasons for doing this?
A
Twin pregnancies can often result in:
- Early fetal resorption or loss
- Late-term abortions
- Birth of small, growth-retarded foals
- Foaling difficulties in mares aborting twins in late gestation
- Difficulty rebreeding after late-term abortion
13
Q
In October, two horses near Brisbane (AUS) show acute onset of respiratory distress, fever, and depression. Their caretaker also develops signs of respiratory disease. A roost tree for bats is found in the horses’ pasture.
What is the most likely etiology?
A
Equine Hendra virus
(Henipavirus, Paramyxovirinae)
This virus was first identified in 1995 and can be fatal for both horses and humans.
14
Q
Several horses show sudden onset of hyperexcitability, ataxia, sweating, tachycardia, dyspnea, pyrexia, and death. On post-mortem, hemorrhage is present in skeletal and cardiac muscle. A “supplement” was given IV two to three hours prior to onset.
What is the most likely etiology?
A
Acute selenium toxicosis
15
Q
Placentitis in the mare is commonly a result of:
- A. Ascending infection through the cervix
- B. Hematogenous spread of bacteria from the gastrointestinal tract
- C. Primary infection of the fetus that spreads to the placental tissues
- D. Septicemia
A
A. Ascending infection through the cervix
16
Q
Lameness in horses is graded on a 5-point scale. What defines a grade 4 out of 5 lameness?
A
Consistently observable lameness at a walk
17
Q
Signs of coital exanthema in the stallion include the following, except:
- A. Paraphimosis and inability to breed if untreated
- B. Raised pink ulcerations on the shaft and glans of the penis
- C. Similar lesions around the vulva of the mare
- D. Unwillingness to breed due to pain
A
A. Paraphimosis and permanent inability to breed if the condition is untreated
The remainder are signs of equine coital exanthema (caused by equine herpesvirus-3).
18
Q
A horse that is housed indoors without access to fresh grass shows generalized weakness, fatigue, and weight loss despite normal appetite. It spends an unusual amount of time lying down. Serum vitamin E levels are low.
What should be your next diagnostic test?
A
Muscle biopsy of the sacrocaudal dorsomedial muscle at the base of the tail
(to diagnose equine motor neuron disease)
Histopathology identifies denervation atrophy.
19
Q
What is the most common cause of colic in an otherwise healthy newborn foal?
A
Meconium impaction
Usually responds to enemas, rarely requires surgical intervention.
20
Q
On skull radiographs of a horse with a draining tract in the region of the external auditory meatus, you see a mineralized mass that has the appearance of a tooth.
What is the diagnosis?
A
A dentigerous cyst
(a.k.a. temporal teratoma or “ear tooth”)
21
Q
Endometritis in the mare is usually due to any of the following bacteria except:
- A. Bacillus spp.
- B. Escherichia coli
- C. Pseudomonas spp.
- D. Streptococcus zooepidemicus
A
A. Bacillus spp.
The others are all associated with endometritis.
22
Q
What are the names of the joint pouches in the equine stifle and which ones communicate?
A
Joint pouches:
- Femoropatellar
- Medial femorotibial
- Lateral femorotibial
Communications:
- The femoropatellar and medial femorotibial almost always communicate.
- The femoropatellar and the lateral femorotibial communicate ~25% of the time
- The medial and lateral femorotibial pouches almost never communicate
It is important to know joint communications for wound evaluation or administration of therapeutics.
23
Q
On radiographs, you see a well-circumscribed dermal mass, with granular mineralization and no bony involvement, adjacent to the tarsus of an Arabian stallion.
What is the most likely diagnosis?
A
Equine mast cell tumor
This is a benign tumor which is not associated with lameness and is curative with excision.
24
Q
When palpating a mare during estrus, the uterus is:
- A. Easily defined due to uterine edema
- B. Easily retractable into the pelvic canal due to relaxation of the broad ligament
- C. Lacking tone and may be difficult to find
- D. Not easy to reach due to relaxation of the broad ligament
A
C. Lacking tone and may be difficult to find
This is the result of the effects of estrogen on uterine tone.
25
Equine multinodular pulmonary fibrosis (**EMPF**) has been **associated** with which **infectious** agent?
Equine herpesvirus-5
| (EHV-5)
## Footnote
EHV-5 is associated but lacking evidence as to whether it is causative, related, or incidental.
26
What is the optimal serum concentration of **IgG** in a 24-hour-old **foal**?
Over 800 mg/dl
## Footnote
Failure of passive transfer is < 400 mg/dl and 400-800 mg/dl is a grey area.
27
**Synchronous diaphragmatic flutter** (a.k.a. "thumps") in horses is suggestive of which serum **biochemical** abnormality?
Hypocalcemia
28
When sampling the **lower respiratory tract** of a horse with suspected bacterial pneumonia, which **diagnostic procedure** is preferred for obtaining a **culture** sample?
Tracheal aspiration
| (transtracheal or endoscopic)
## Footnote
Bronchoalveolar lavage is for cytology only.
29
When a standing **lateral thoracic radiograph** of a horse is taken, which lung is **most clearly** seen?
* A. The lung field closest to the cassette
* B. The opposite lungfield
A. The lung field closest to the cassette
## Footnote
The opposite lung field gets distorted due to the great width of the equine chest.
30
On **radiographs** of the equine **tarsus**, where are the two most **common locations** of **osteochondrosis**?
1. Cranial aspect of the distal intermediate ridge of the tibia (a.k.a. "DIRT" lesion)
2. Lateral trochlear ridge of the talus
31
The **migrating larvae** of this parasite can cause **thrombosis of mesenteric arteries** in horses.
*Strongylus vulgaris*
32
**Nigropalladial encephalomalacia** (also called necrosis of the substantia nigra) is the characteristic lesion of which **plant toxicosis** in horses?
Yellow star thistle (*Centaurea solstitialis*) or Russian knapweed (*C. repens*)
| (commonly found in California and other arid regions)
33
A mare presents with a history of stallion-like behavior and a large ovarian mass, which on cut surface is cystic.
**What is the likely diagnosis?**
Granulosa cell tumor
## Footnote
Diagnose with ultrasound (affected ovary is large and honey-combed) and confirm with blood testing (AMH, inhibin, and testosterone).
34
Which **etiologic** agent is associated with **equine sarcoids**?
Bovine papilloma virus 1 and 2
35
Which **bacterium** is commonly associated with **ulcerative enterocolitis** and **granulomatous bronchopneumonia** in **foals**?
*Rhodococcus equi*
36
The optimal therapeutic regimen for **rhodococcal pneumonia** in foals consists of treatment with **which antimicrobial(s)**?
A macrolide (erythromycin, azithromycin, or clarithromycin) combined with rifampin
37
Which nerve is anesthetized to **block motor function** to the **eyelid** of a horse undergoing an **ophthalmic exam**, and from which cranial nerve does this originate?
Auriculopalpebral nerve, a branch of the facial nerve (CN VII)
| (blocks the orbicularis oculi muscle)
38
In a case with **angular limb deformity**, what does the term "**valgus**" mean?
Lateral deviation of the limb distal to the origin of the deformity
39
The adult third incisors and canine teeth are beginning to erupt in a stallion.
**Approximately how old is this animal?**
Four to five years of age
## Footnote
Adult incisors 1, 2, and 3 erupt at approximately 2.5, 3.5, and 4.5 years of age, respectively. Canines erupt at 4-5 years.
40
A pacer mare finishes far behind the field and on physical examination has an irregularly irregular heart rhythm.
**What is the most likely diagnosis?**
Atrial fibrillation
## Footnote
The most common pathologic equine arrhythmia.
41
Viborg's triangle is an important anatomical landmark in horses as it outlines a surgical approach to the guttural pouch.
**What are its boundaries?**
1. Ramus of the mandible
2. Tendon of sternocephalicus
3. The linguofacial vein
42
Which two **organ systems** are affected when horses sustain toxicosis by ingesting **red maple leaves**?
1. Hematologic
2. Renal
## Footnote
Oxidative injury to red blood cells causes hemolysis and pigment nephropathy/renal failure.
43
What is **Galvayne's groove**?
A longitudinal groove in the **upper third incisor** of older horses
| (usually visible between ages 10 and 30 years)
## Footnote
It is relatively unreliable for use in aging horses.
44
Mares with which **blood group** characteristics are at risk for producing a foal with **neonatal isoerythrolysis**?
Mares negative for either or both the Aa and Qa antigens
45
Describe the classic serum **biochemical abnormalities** in an untreated foal with **uroperitoneum**.
* Hyponatremia
* Hypochloremia
* Hyperkalemia
* Azotemia
## Footnote
Hospitalized foals in IV fluids that develop uroperitoneum may not show the classic abnormalities.
46
Which equine disorder is also known as "**shaker foal syndrome**"?
Botulism
| (*Clostridium botulinum* infection)
47
An older horse is diagnosed with a diastolic, decrescendo murmur on the left side during routine physical exam.
**What is the most likely etiology?**
Aortic regurgitation/aortic insufficiency
| (age-related valvular degeneration)
## Footnote
This is the most common murmur in older horses.
48
Which **equine herpesvirus** can cause **respiratory** signs, **myeloencephalopathy**, and **abortion**?
Equine herpesvirus-1
| (EHV-1)
49
What is the causative agent of **Tyzzer disease** in foals?
*Clostridium piliformis*
50
What is the etiologic agent of **equine protozoal myeloencephalitis**?
| (EPM)
*Sarcocystis neurona*
## Footnote
And rarely *Neospora hughesii*.
51
**Hematuria after exercise** in the horse is most likely caused by:
Cystic calculi
| (urolithiasis)
52
Which **immune-mediated** ocular disease is one of the most common causes of **blindness** in horses?
Equine recurrent uveitis
| (ERU, "moon blindness")
## Footnote
With chronicity, it can also progress to glaucoma.
53
Which **antimicrobial** drug is most commonly used for the treatment of suspected **anaerobic** bacterial involvement in horses with **pleuropneumonia**?
Metronidazole
54
Which horse **breed** is best known for having a **genetic defect** leading to severe combined immunodeficiency (**SCID**)?
| (SCID)
Arabian
55
What is the most common **adnexal ocular tumor** in the horse, typically seen in breeds such as Belgian, Clydesdale, Appaloosa, and Paint?
Squamous cell carcinoma
## Footnote
This occurs most commonly on unpigmented/white skin.
56
**Atrophy** of which laryngeal muscle leads to **laryngeal hemiplegia** in the horse?
Cricoarytenoideus dorsalis
| (innervated by the recurrent laryngeal nerve)
## Footnote
Horses with left laryngeal hemiplegia are called "roarers" due to the noise they make when exercising.
57
A newborn foal is considered **premature** if it is delivered prior to which gestational age?
320 days
## Footnote
Normal equine gestation in mares lasts around 11 months or 340 days.
58
**Bog spavin** is the common term for chronic distension of **which joint**?
Tibiotarsal
| (joint capsule of the hock)
## Footnote
This causes a swelling of the dorsomedial aspect of the hock joint.
59
**Pneumovagina** in the mare is associated with chronic inflammation and infection of the reproductive tract. It is **associated with**:
* A. The long vaginal tract in large mares
* B. A wide pelvis
* C. Excessive body condition
* D. Poor perineal conformation
D. Poor perineal conformation
60
Which of the following is a commercially available **luteinizing hormone agonist** that can be used for **hastening ovulation** in the mare?
* A. Altrenogest
* B. Epinephrine
* C. Follicle stimulating hormone
* D. Human chorionic gonadotropin
D. Human chorionic gonadotropin
| (hCG)
## Footnote
It is only effective when administered to mares with follicles ≥ 35 mm.
61
A horse who has all **deciduous incisors** can be said to be less than **what age**?
2.5 years
## Footnote
Permanent incisors 1, 2, and 3 erupt at approximately 2.5, 3.5, and 4.5 years of age, respectively.
62
A six-month-old filly presents for dyspnea with a large, nonpainful, turgid, gas-filled swelling in the throatlatch area.
**What is the most likely diagnosis?**
Guttural pouch tympany
63
**Purpura hemorrhagica** is most often a sequela of which equine **bacterial infection**?
Strangles
| (*Streptococcus equi* sbsp. *equi*)
## Footnote
Purpura is seen ~ two to four weeks after exposure. It is a type III hypersensitivity reaction.
64
There is a **class of antibiotics** that are more commonly used as feed additive growth promoters in ruminants or to prevent coccidiosis in ruminants/poultry. They cause **myocardial necrosis** in horses that accidentally ingest it. What is it?
Ionophores
65
A weanling horse presents with diarrhea, ventral edema, and severe hypoproteinemia with hypoalbuminemia.
**What is the top differential diagnosis?**
*Lawsonia intracellularis* infection
| (equine proliferative enteropathy)
## Footnote
It is seen almost exclusively in weanling age foals.
66
During the **carrier** state, **equine arteritis virus** is solely present in **which organ** system in **stallions**?
The reproductive tract
67
Which statement about equine **laminitis** is **true**?
* A. Digital pulse of an affected foot is often reduced and extremity is cool to touch
* B. Hoof care includes application of pads to redistribute weight-bearing to frog-heels
* C. The gold standard treatment is systemic corticosteroids
B. Hoof care [often] includes application of pads that redistribute weight-bearing to frog-heels
## Footnote
Takes weight off the solar margin/toe where the laminae are usually most-affected.
68
In horses, **laryngeal hemiplegia**/roaring typically is an idiopathic condition affecting which **nerve** on which side?
Left recurrent laryngeal nerve
## Footnote
It is longer than the right and thus thought to be more prone to damage.
69
A horse presents with a strange gait. With each step, there is excessive flexion of the hindlimbs, with the hoof almost touching the belly. It goes away at a trot.
**What is this condition called?**
This is stringhalt
## Footnote
Often worse when horse is backed, but goes away at a trot or canter.
70
**Bacterial pneumonia** in adult horses is most commonly associated with which **organism**?
*Streptococcus equi* sbsp. *zooepidemicus*
## Footnote
*S. zooepidemicus* is commensal in the upper respiratory tract and thus opportunistic infection is common.
71
A three-month-old foal is presented in respiratory distress, with a WBC count of 23,500 cells/μl and a fibrinogen of 600 mg/dl.
**What is the most likely etiology in this case?**
*Rhodococcus equi* pneumonia
72
Normal foals (< three months of age) consume approximately **what percentage** of their **body weight** in **milk per day**?
20-27%
73
It is August in the mid-Atlantic region of the U.S. and a six-year-old Quarter horse gelding presents with acute, severe diarrhea; depression; and high fever.
**What is the primary initial rule-out?**
*Neorickettsia risticii* infection
| (Potomac horse fever)
74
What is the cause of **equine coital exanthema**?
Equine herpesvirus-3
## Footnote
There is no specific treatment - isolate affected animal, do not breed until lesions heal, and administer topical antibacterials to prevent secondary infection.
75
In horses, which **endocrinopathy** is associated with **hypertrichosis** due to failure of seasonal haircoat shedding?
Pituitary pars intermedia dysfunction
| (a.k.a. equine Cushing disease)
76
Name two **risk factors** for **enterolith** formation in horses.
* High alfalfa content in hay
* Decreased daily access to pasture grasses
* Breed (Arabians are over-represented, which may be related to geographical prevalence)
* Geography (California, Arizona, and other arid western U.S. regions)
* Hard water (high in magnesium, calcium, and phosphate)
77
Which **heritable muscle disease** of Quarter horses is characterized by episodes of **muscular fasciculations and weakness**?
Hyperkalemic periodic paralysis
| (HYPP)
78
Within how many **hours of birth** should a neonatal foal be able to **stand**?
Within one hour
## Footnote
Remember the "1-2-3" rule. Healthy foals following normal parturition should: stand within one hour, nurse within two hours, and mare should pass fetal membranes (placenta) within three hours.
79
What is the **mean gestational length** of the mare?
Average is about 11 months
| (or 338-343 days)
80
Infection with *Streptococcus equi* sbps. *equi* can result in **pharyngeal obstruction** after abscessation of **which lymph nodes**?
Retropharyngeal lymph nodes
## Footnote
This is what gives the disease the name "strangles."
81
Which **drug** has a reported risk of unwanted penile prolapse (**paraphimosis**) in the horse (and thus is avoided for use in stallions)?
Acepromazine
## Footnote
Very uncommon but reported and thus important to consider when making sedation/anesthesia protocols for breeding stallions.
82
Which **nerve deficits** to the head can occur as a result of **guttural pouch mycosis** in horses?
* Laryngeal paralysis (X)
* Dysphagia (IX and X)
* Dorsal displacement of the soft palate and other pharyngeal deficits (IX and X)
* Facial nerve paralysis (VII)
* Horner syndrome (sympathetic fibers)
* Head tilt/vestibular syndrome (VIII)
## Footnote
Nerves VII and VIII run in the wall of the GP, and nerves IX through XII run directly through it.
83
What are the **radiographic** signs of **chronic laminitis** in the horse?
* Rotation and/or vertical displacement (sinking) of P3 from the hoof wall
* Osteolysis of solar margin of P3
* Remodeling (periosteal proliferation) of dorsodistal P3
* Pathologic P3 fracture
84
What is the major **problem** associated with **prophylactic** use of penicillin in horses exposed to ***Streptococcus equi* sbsp. *equi*** but not showing clinical signs?
Horses remain **highly susceptible to disease** following discontinuation of therapy
| (because they do not mount an immune response)
## Footnote
vs. after resolution of natural infection they have immunity that lasts ~ five years.
85
**Hypoventilation** in a horse under general anesthesia can produce which type of **acid/base disturbance**?
Respiratory acidosis
| (due to hypercarbia or high CO2)
86
A 15-year-old horse presents with a chronic cough, exercise intolerance, and increased abdominal muscle effort on expiration (“heave line”). Wheezing is noted on auscultation, and tracheal endoscopy shows moderate mucus accumulation.
**Which diagnostic test will confirm the top differential?**
Bronchoalveolar lavage (BAL) is the diagnostic of choice
| (see increased inflammatory cells [neutrophils>mast cells, etc.], mucus)
## Footnote
The signs are consistent with equine asthma (formerly known as "recurrent airway obstruction" or "heaves")
87
Which **muscle disorder** of horses is associated with an abnormal accumulation of **glycogen stored** in muscle and increased **insulin sensitivity**?
Polysaccharide storage myopathy
| (PSSM)
## Footnote
PSSM 1 has known heritability in Quarter horse breeds. PSSM 2 has unknown etiology, seen in Quarter horses, Warmbloods, and Arabians.
88
The most common **ovarian neoplasm** in the mare is:
* A. Cystadenoma
* B. Dysgerminoma
* C. Granulosa cell tumor
* D. Teratoma
C. Granulosa cell tumor
89
The expected rate of **growth** for an ovarian **follicle** in the mare is:
* A. 11-12 mm/day
* B. 8-9 mm/day
* C. 6-8 mm day
* D. 2-5 mm/day
D. 2-5 mm/day
## Footnote
This knowledge helps time breeding.
90
What is the etiology of **equine motor neuron disease**?
Chronic vitamin E deficiency
## Footnote
Primarily seen in middle-aged adult horses kept on dry lots or stables with no access to green forage or pasture for ≥18 months.
91
Name **two species of mites** that can infect horses.
* *Sarcoptes scabiei*
* *Chorioptes equi*
* *Psoroptes equi*
## Footnote
*Pyemotes tritici* is another mite that causes "straw itch."
92
Which of the following is the best-recognized **risk factor** for **epiploic foramen entrapment** of the small intestine in horses?
* A. Breed
* B. Crib-biting
* C. High concentration of sand in the feed
* D. Pain
* E. Physical inactivity
B. Crib-biting
## Footnote
The reason is unclear, but changes in abdominal pressure as the horse sucks in air have been proposed as part of the disease mechanism.
93
A foal treated for *R. equi* pneumonia with a standard antibiotic protocol develops diarrhea. **Which is true?**
* A. Diarrhea is usually self-resolving
* B. Gentamicin is a good alternative
* C. Treatment should be changed to macrolide monotherapy
A. Diarrhea in this context is usually self-resolving
## Footnote
Gentamicin does not penetrate into Rhodococcal abscesses, even with susceptible bacteria (B), and macrolide monotherapy is ineffective (C).
94
Why are **seasonally adjusted reference ranges** required when testing horses for **PPID** (Cushing disease) using **plasma ACTH** concentrations, and during **which months** is this adjustment most critical?
ACTH levels naturally rise in late summer and autumn, causing false positives if non-seasonal reference ranges are used
| (this makes autumn a great season for a natural dynamic test)
## Footnote
Use adjusted reference intervals or laboratory-specific cut-offs during this period to ensure accurate diagnosis.
95
What are the **two** most common disorders that cause **sinusitis** in the horse?
* Dental disease (maxillary cheek tooth root abscessation) is most common, causing secondary sinusitis
* Upper respiratory disease (primary sinusitis) is second-most common
## Footnote
Other causes of secondary sinusitis include sinus disorders like paranasal sinus cyst, neoplasia, ethmoid hematoma.
96
What is a proven way to **mitigate** the **risk** of **SIRS-associated laminitis** in horses with endotoxemia?
## Footnote
i.e., from colitis, metritis, or pleuropneumonia
Cryotherapy
| (i.e., continuous distal limb cooling)
## Footnote
It is the only intervention with strong experimental/clinical evidence for preventing SIRS-associated laminitis.
Additional therapeutic measures address endotoxemia, pain, inflammation, and the underlying disease process.
97
Upon endoscopic examination of a horse with a history of exercise intolerance and respiratory stertor, you cannot visualize the free border of the epiglottis.
**What are the top differential diagnoses?**
Epiglottic entrapment and dorsal displacement of the soft palate
| (both obscure the scalloped edge of the epiglottis)
## Footnote
Severe pharyngeal collapse also precludes visualization, but the horse would likely collapse due to complete airway obstruction.
Encouraging the horse to swallow while viewing the pharynx/epiglottis endoscopically typically allows definitive diagnosis, if unclear.
98
A horse presents for acute onset of left-sided head tilt, a drooping left ear, left-sided ptosis, and drooping of the muzzle on the left. During endoscopy of the left guttural pouch, you notice bony proliferation of the stylohyoid bone as well as hyperemia of the surrounding mucosa.
**What is the diagnosis?**
Temporohyoid osteoarthropathy
99
Several horses in a barn show signs of respiratory disease, including coughing and nasal discharge. One mare aborts her foal in the eighth month of gestation. Two horses have pelvic limb weakness and decreased tail tone.
**What is the most important action?**
Call the state/provincial vet
| (top differential is equine herpes myeloencephalopathy [EHM])
## Footnote
EHM is reportable in North America and the barn will be quarantined until proven negative.
Next step likely is taking samples (whole blood, nasal swabs, aborted tissues) for PCR testing.
100
A horse has alopecia and crusting on the ventral abdomen and tailhead; it is extremely pruritic. The owner reports that this problem seems to occur every year during the warm months and improves if the horse is kept inside.
**What is the most likely diagnosis?**
Insect hypersensitivity
| (due to *Culicoides* spp.)
101
At what age do the **testicles** of a male horse **descend**?
Within a few days after birth
| (typically by one to two weeks of age in most colts)
## Footnote
Occasionally up to one month post-partum. Failure of one or both testes to descend by six to 12 months of age is considered cryptorchidism.
102
At approximately what **diameter** (in millimeters) does a preovulatory follicle typically **ovulate** in a cycling mare?
> 35 mm
| (with slight variation depending on breed, age, and individual mare)
## Footnote
Knowing this helps time breeding.
103
Regarding use of **progesterone** or altrenogest in the mare, which is **FALSE**?
* A. They may be used for synchronizing estrus
* B. They increase uterine contractions during labor
* C. They may be used to suppress estrous behavior
* D. They suppress follicular development and ovulation
B. They increase uterine contractions during labor
## Footnote
Progesterone causes uterine quiessence to maintain diestrus or pregnancy (so not causing contractions).
The others are true: it can be used to synchronize or suppress estrus and suppress follicular development and ovulation.
104
Why is **gastric decompression** essential when treating a horse with **duodenitis-proximal jejunitis** (a.k.a. anterior enteritis, proximal enteritis)?
Prevents gastric distension and rupture (usually fatal) and reduces pain caused by the accumulation of enterogastric reflux
105
**Without imaging**, what can you measure to **diagnose** a **180-day pregnancy** in a miniature mare?
* A. eCG (from endometrial cups)
* B. Estrone sulfate (from feto-placental unit)
* C. Pregnancy-specific protein B (from binucleated trophoblastic cells of the placenta)
* D. Progesterone (from corpus luteum)
B. Estrone sulfate
## Footnote
Produced by the feto-placental unit, estrone sulfate is a good indicator of fetal viability after day 90.
Also, at 180 days' gestation, you should also be able to visualize the fetus on transabdominal ultrasound.
106
A two-year-old stallion rears and **falls backwards**. The horse is at risk for **fracture of which bone(s)** that lead to **neurological** signs?
Basisphenoid and basioccipital bones
| (where rectus capitis ventralis and longus capitis insert at skull base)
## Footnote
Fractures here often cause brainstem trauma leading to ataxia or sudden death.
107
What is the diagnostic **purpose** of placing a **rebreather bag** over the mouth of a horse?
Optimizes detection of abnormal lung sounds
| (by increasing respiratory rate and tidal volume)
108
**When** would you expect to see **reticulocytes** in the blood of horses?
Never
## Footnote
Horses do not release measurable reticulocytes from the bone marrow, so it is not currently a useful method for evaluating anemia.
109
Which **radiographic view** is preferable for imaging a horse's **left fourth metacarpal bone**:
* A. Dorsomedial-to-plantarolateral oblique (DMPLO)
* B. Dorsolateral-to-plantaromedial oblique (DLPMO)
B. Dorsolateral-to-plantaromedial oblique (DLPMO)
## Footnote
The source of the beam is in front of the horse (cranial) and to its outside (lateral), which highlights ("exteriorizes") the left fourth metacarpal on the radiograph (and "hides" the left second metacarpal).
110
In the adult horse, **normally concentrated** urine should have a specific gravity (**USG**) greater than which value?
1.025
111
In **radiographs** of the **cervical spine** in the horse, which vertebrae are **distinct** in appearance and must be included in the views in order to verify location?
* C1 (the atlas)
* C2 (the axis)
* C6
* C7
## Footnote
C1 has wings, C2 has a spine, C6 has flatter/more parallel transverse processes (look like "sled runners"), and C7 is shorter and often has a small dorsal spinous process.
112
A mare aborts a nine-month-old fresh (minimally autolyzed) fetus with no premonitory clinical signs. Necropsy of the fetus reveals multifocal pinpoint hepatic necrosis and severe pulmonary edema.
**What is the most likely cause of abortion?**
Equine herpesvirus-1
| (EHV-1)
## Footnote
The most common infectious cause of abortion in horses.
113
What is the most likely causative agent of **pectoral abscesses** in a horse in Texas or California?
*Corynebacterium pseudotuberculosis*
| (the causative agent of "pigeon fever")
114
What is the **test** of choice for **equine infectious anemia**?
The Coggins test
| (AGID)
## Footnote
It detects antibodies to the virus and is required for regulatory and import/export purposes.
115
A horse that has been kept in a muddy paddock has bilateral hindlimb lameness. On examination you find the frog of both feet has foul-smelling black exudate.
**What are the most likely diagnosis and etiologic agent?**
Necrotizing pododermatitis (thrush); caused by *Fusobacterium necrophorum*
116
An eight-month-old foal has swollen joints and **radiographically flared physes** of the distal radius. What is the recommendation on how this could have been **prevented**?
Prevent physitis with a focus on controlling growth rate with balanced nutrition (avoiding excessive energy and maintaining proper calcium:phosphorus ratio).
## Footnote
Seen in fast-growing, well-muscled foals during the season when ground is hard.
117
A horse presents with acute unilateral blepharospasm, photophobia, and corneal edema. Fluorescein stain is positive.
**What is the appropriate treatment approach?**
* Topical antimicrobials
* Atropine
* Anticollagenases (e.g., serum, EDTA)
* Systemic NSAIDs
## Footnote
Consider antifungals and a subpalpebral lavage system for severe or refractory cases.
Never use topical steroids on an ulcerated cornea.
118
Name **three** of the hallmark **clinical signs** of **acute equine uveitis**?
* Epiphora
* Blepharospasm
* Corneal edema
* Episcleral congestion
* Aqueous flare
* Fibrin within the anterior chamber
## Footnote
Chronic signs include cataracts, posterior synechiae, iris color change/thinning, lens luxation, glaucoma, and phthisis bulbi.
119
What is the main **etiology** associated with **equine recurrent uveitis**?
| (ERU)
Most often immune-mediated
## Footnote
It may follow infection with *Leptospira interrogans*; other pathogens and trauma have also been implicated.
120
What is the most useful preliminary diagnostic **test** for identifying an **infectious** cause of **acute colitis** in horses?
Fecal PCR panel for pathogens such as:
* *Salmonella* spp.
* *Clostridium perfringens* (toxins)
* *Clostridioides difficile* (toxins)
* *Neorickettsia risticii* (Potomac horse fever)
* Coronavirus
| (PCR is rapid and sensitive)
## Footnote
Also submit: culture to determine which *Salmonella* spp. with what sensitivity is present, when needed; toxin assay for *Clostridium*.
121
In **septic foals**, name two of the **organ systems** most commonly affected.
* Musculoskeletal (septic joints)
* Gastrointestinal (diarrhea)
* Respiratory (pneumonia)
* Umbilical (omphalophlebitis)
## Footnote
Sepsis in foals often presents with multi-system involvement, reflecting hematogenous spread of bacteria, often associated with failure of passive transfer.
122
A three-day-old foal on the farm is lethargic, not nursing, and has a markedly swollen joint. **Which is the most appropriate step for the best outcome?**
* A. Administer oral antibiotics on the farm and monitor
* B. Give IV fluids and anti-inflammatories and recheck in 48 hours
* C. Immediate referral to a veterinary hospital for aggressive sepsis management
* D. Perform joint lavage on the farm
C. Immediate referral to a veterinary hospital for aggressive sepsis management
## Footnote
Foals with suspected septic arthritis and systemic illness require urgent hospital workup and care, including: IV fluid therapy and antimicrobials, joint lavage/local antibiotics, nutritional support, antiinflammatories/analgesics, etc.
123
A **horse** presents after a suspected episode of exertional rhabdomyolysis (“**tying up**”). **When** should blood be drawn to confirm the diagnosis, and what are the most important immediate **treatment** considerations?
* A. Draw blood immediately; start high-starch feed and exercise
* B. Draw blood 4–6 hours after the onset of clinical signs; provide analgesics, vasodilators, and IV fluids as needed
* C. Draw blood 24 hours later; restrict water and electrolytes
* D. No need to draw blood; start corticosteroids immediately
B. Draw blood 4–6 hours after the onset of clinical signs; provide analgesics, vasodilators, and IV fluids as needed
## Footnote
Muscle enzyme levels begin to increase 4-6 hours after onset, and acute treatment focuses on pain relief, circulation support, and preventing renal complications from myoglobinuria.
124
What is the most important **preventive measure** to reduce the risk of **sepsis** in neonatal **foals**?
Prevent failure of passive transfer
## Footnote
Adequate colostral IgG within ≤ 24 hours of birth provides essential immune protection against systemic infection.
125
Which **parasite** is the most common cause of **diarrhea** and **weight loss** due to large intestinal damage in **adult horses**?
* A. *Strongylus vulgaris*
* B. *Parascaris equorum*
* C. Cyathostomes (small strongyles)
* D. *Anoplocephala perfoliata*
C. Cyathostomes (small strongyles)
| (currently the primary target of parasite programs in adult horses)
## Footnote
Encysted cyathostome larvae emerge from the intestinal wall, causing colitis, diarrhea, and weight loss in adult horses.
126
What is the **intermediate host** of *Anoplocephala perfoliata* (**equine tapeworm**)?
Oribatid mites
## Footnote
Horses become infected by ingesting pasture mites that contain tapeworm cysticercoid larvae.
127
During infection with ***Parascaris equorum*** in foals, **where** do the larvae migrate before returning to the intestines, and what is the approximate **prepatent period**?
* Larvae of the equine roundworm migrate through the liver and lungs
* Prepatent period is ~10–12 weeks
## Footnote
This explains the possibility of respiratory signs (primarily cough, nasal discharge) and increased liver enzymes during migration. They then mature in the small intestine.
128
A five-month-old foal develops acute colic and small intestinal impaction shortly after deworming with ivermectin.
**What is the prognosis in this situation?**
Guarded because rapid die-off of adult *Parascaris* worms after deworming can form an obstructive mass in the small intestine, requiring intensive surgical intervention
## Footnote
Historically, reported survival is poor but recent literature suggests significantly improved survival rates with surgery.
129
How is infection with *Oxyuris equi* (**equine pinworm**) typically **diagnosed**?
A tape test to collect eggs from the perianal region (examined microscopically)
## Footnote
Female pinworms lay sticky eggs around the anus that adhere to the skin rather than being passed in the feces.
130
# True or False:
In **gray** horses > 10 years old, **melanomas** are typically locally aggressive but rarely metastasize.
TRUE
| (common: under tail, parotid salivary gland, peri-anal/perineal, lips)
## Footnote
Gray horse melanomas usually grow slowly and remain local, but they can aggressively invade nearby tissues and only uncommonly spread to distant sites.
131
Name two common **predilection sites** for **melanomas** in aging **gray** horses.
* Under the tail
* Perineum
* Lips
* Prepuce
* Eyelids
* Parotid salivary glands
* Perineal/peri-anal
* Guttural pouches
| (though they can develop anywhere)
132
What is the best **antemortem test** for diagnosing **West Nile virus** in **horses**?
IgM capture ELISA
| (not affected by vaccination)
## Footnote
This test detects recent WNV infection by identifying virus-specific IgM antibodies in serum.
133
A seven-year-old horse presents in late summer with ataxia, muscle fasciculations of the face and neck, hyper-reactivity, and mild colic. Fever is noted.
**What is the top differential diagnosis?**
West Nile virus infection
## Footnote
These signs (ataxia, cranial nerve involvement, fasciculations, hyper-reactivity, +/- fever) are classic for WNV in horses, especially during mosquito season.
134
# True or False:
Eastern, Western, Venezuelan equine encephalitis viruses, and West Nile virus can all **infect humans** and potentially cause neurologic disease.
TRUE
| (all four are zoonotic arboviruses transmitted by mosquitoes)
## Footnote
Humans can become infected, and while many infections are mild or asymptomatic, they can sometimes lead to neurologic disease such as meningitis, encephalitis, or flaccid paralysis.
135
Among the **equine alphavirus encephalitides** (Eastern [EEE], Western [WEE], and Venezuelan [VEE]), which generally has the **best prognosis** in horses?
Western equine encephalitis virus
| (WEE)
## Footnote
It is typically less pathogenic than EEE and VEE, with lower mortality (<50%) and a better overall prognosis in infected horses. Mortality for EEE and VEE reach up to 95% and 83%, respectively.
136
What is the most common **laboratory** finding during an acute phase of **equine infectious anemia** (EIA) infection?
Thrombocytopenia
| (not anemia!)
## Footnote
During the initial one- to three-day febrile phase of EIA, platelet counts typically fall markedly.
137
A horse tests **positive** for equine infectious anemia (EIA) by **Coggins** test. What is the recommended course of action?
* A. Isolate the horse and provide supportive care only
* B. Euthanize or permanently quarantine in a USDA-approved facility
* C. Immediately vaccinate and return to the herd after second vaccine in four weeks
* D. Treat with antibiotics and monitor
B. Euthanize or permanently quarantine in a USDA-approved facility
## Footnote
EIA-positive horses are lifelong carriers and can transmit the virus via biting flies. USDA regulations require euthanasia or strict quarantine to prevent spread.
138
When a **racehorse** sustains a severe **suspensory ligament** injury, which **adjacent structure** is commonly also damaged?
The proximal sesamoid bones
## Footnote
Severe suspensory ligament injuries often involve avulsion or fracture of the proximal sesamoid bones due to their close anatomical and functional relationship.
139
In a **horse** with a **distal limb** fracture, what is the proper **alignment** of the limb when applying a **dorsal splint**?
Position the limb with the dorsal cortices of the bones aligned and the toe pointed (with heel lifted)
## Footnote
Keeping the bones aligned along their dorsal surfaces maintains the limb’s normal weight-bearing axis, helps prevent fetlock collapse, minimizes soft tissue strain, and stabilizes the fracture for safe transport.
140
A two-year-old Thoroughbred stallion becomes acutely lame after a workout, with marked fetlock effusion.
**What is the most likely top differential diagnosis, which is diagnosed with radiographs?**
Distal third metacarpal condylar fracture
| (lateral condyle most common)
## Footnote
Acute post-exercise lameness with fetlock swelling in young racehorses is highly suggestive of a condylar fracture; lateral condyles are more commonly affected, and radiographs confirm the diagnosis.
141
What is **“bucked shins”** in **racehorses** and what causes it?
A painful inflammation of the dorsal surface of the third metacarpal bone (cannon bone) caused by repetitive high‑strain cyclic loading in young racehorses
## Footnote
When intense speed work loads a bone that has not fully adapted, microfractures and periosteal elevation occur, leading to the lameness and swelling.
142
A horse presents acutely lame on one limb, with a strong digital pulse and localized pain on hoof tester examination.
**What is the most appropriate initial treatment?**
1. Hoof paring to locate and drain the abscess (if possible)
2. Application of a poultice
3. NSAIDs for pain
## Footnote
Often the poultice needs to be in place for a couple of days to enhance abscess maturation prior to identifying it for drainage.
143
What is the treatment of choice for **equine squamous gastric ulcers**?
Proton pump inhibitors
| (specifically omeprazole)
## Footnote
Combine with management changes.
144
Name **two** common risk factors for **equine gastric ulcer syndrome**.
| (EGUS)
* High-intensity exercise or training
* Frequent transport
* Stall-confinement
* Intermittent feeding or fasting
* High-grain/low-forage diet
* Stress from competition or social disruption
* Concurrent illness or NSAID use
## Footnote
These factors increase gastric acid exposure or reduce mucosal protection, making the horse more susceptible to squamous or glandular ulceration.
145
What is the definitive method to diagnose **glandular gastric ulcers** in horses?
Fasting gastroscopy
## Footnote
Allows direct visualization of the pyloric and glandular mucosa, which is necessary because clinical signs alone are nonspecific.
146
What is the most common **complication** of **equine esophageal obstruction**?
Aspiration pneumonia
| (because feed or saliva can enter the lungs)
## Footnote
Other possible complications include esophageal stricture, esophageal rupture, and diverticulum formation.
147
A four‑year‑old Thoroughbred racehorse presents with a history of exercise intolerance and a loud inspiratory “roaring” noise during fast gallops. On endoscopy, the left arytenoid cartilage fails to abduct fully.
**What is the indicated treatment?**
Surgical prosthetic laryngoplasty
| (“tie‑back” procedure)
## Footnote
This permanently abducts the arytenoid cartilage to improve airflow and reduce the noise.
148
A three‑year‑old Thoroughbred racehorse develops a loud gurgling noise during fast exercise, and dynamic endoscopy reveals the caudal edge of the soft palate positioned dorsally over the epiglottis.
**What is the diagnosis?**
Dorsal displacement of the soft palate
| (DDSP)
## Footnote
The soft palate moves above the epiglottis during exercise, partially obstructing the airway and causing the characteristic expiratory gurgling noise.
149
An adult horse presents with unilateral epistaxis. Name **two** possible causes of **epistaxis** in the horse.
* Trauma (fracture of sinus or skull bones)
* Exercise‑induced pulmonary hemorrhage (EIPH)
* Guttural pouch mycosis
* Progressive ethmoid hematoma
* Sinusitis with erosion of vessels
* Coagulopathy
* Foreign body in the airway
* Neoplasia
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