NAVLE Small Ruminant Medicine (Sheep and Goats) — Questions and Answers
Question 1: A 3-year-old dairy goat presents with progressive weight loss, decreased milk production, and bilateral carpal swelling. Lung auscultation reveals diffuse crackles. Cerebrospinal fluid analysis shows mononuclear pleocytosis. The most likely diagnosis is:
- Caseous lymphadenitis (Corynebacterium pseudotuberculosis)
- Caprine Arthritis Encephalitis (CAE) virus infection (Correct answer)
- Mycoplasma mycoides subsp. capri polyarthritis
- Maedi-Visna virus infection
Correct answer: Caprine Arthritis Encephalitis (CAE) virus infection
CAE virus (a lentivirus) in adult goats classically presents as chronic progressive polyarthritis (especially carpal joints) combined with interstitial pneumonia and occasional leukoencephalomyelitis. Maedi-Visna is the sheep equivalent but does not cause arthritis as prominently. Caseous lymphadenitis causes abscessation, not arthritis + pneumonia. Mycoplasma causes acute febrile arthritis.
Question 2: A flock of sheep presents with sudden deaths in 2-to-6-week-old lambs that were thriving until 24 hours prior. Necropsy reveals hemorrhagic abomasal and intestinal lesions with gas in the intestinal lumen. Gram-positive rods are cultured. The most appropriate preventive strategy for next year's lamb crop is:
- Vaccinate ewes with Clostridium perfringens types C and D toxoid 4–6 weeks before lambing (Correct answer)
- Administer prophylactic penicillin G to all lambs at birth
- Feed sodium bicarbonate free-choice to buffer rumen pH
- Vaccinate lambs at birth with Clostridium novyi type B bacterin
Correct answer: Vaccinate ewes with Clostridium perfringens types C and D toxoid 4–6 weeks before lambing
Overeating disease (pulpy kidney) caused by Clostridium perfringens type D and enterotoxemia type C are the primary clostridial diseases of young lambs. Vaccinating ewes 4–6 weeks pre-lambing ensures high colostral antibody titers that passively protect newborn lambs. Antibiotic prophylaxis at birth is not practical or regulatory-appropriate for herd prevention.
Question 3: A 2-year-old sheep presents with acute blindness, head pressing, and opisthotonus. The animal has been on a high-grain diet with limited forage. Blood thiamine levels are low. Which treatment should be administered immediately?
- Intravenous dextrose 50% at 0.5 mL/kg
- Thiamine (vitamin B1) 10–20 mg/kg IV or IM (Correct answer)
- Dexamethasone 0.1 mg/kg IV to reduce cerebral edema
- Magnesium sulfate IV to treat suspected hypomagnesemia
Correct answer: Thiamine (vitamin B1) 10–20 mg/kg IV or IM
Polioencephalomalacia (PEM) in sheep is caused by thiamine deficiency, often triggered by high-grain diets that favor thiaminase-producing rumen bacteria. Clinical signs include blindness, cortical signs, and opisthotonus. Immediate high-dose thiamine (B1) administration is the treatment of choice. Dextrose worsens thiamine deficiency; dexamethasone is adjunctive at best.
Question 4: Ovine Progressive Pneumonia (OPP) caused by Maedi-Visna virus is best controlled in a flock through which strategy?
- Annual vaccination with killed-virus OPP vaccine
- Test-and-cull seropositive animals combined with separating lambs from seropositive ewes at birth (Correct answer)
- Prophylactic long-term tetracycline administration in feed
- Parenteral ivermectin to eliminate the arthropod vector
Correct answer: Test-and-cull seropositive animals combined with separating lambs from seropositive ewes at birth
Maedi-Visna/OPP is a lentiviral infection with no vaccine or cure. Control relies on identifying seropositive animals via AGID or ELISA and removing them, combined with preventing transmission to lambs via infected colostrum/milk by separating and heat-treating or discarding colostrum. There is no arthropod vector; it is spread by close contact and milk.
Question 5: A goat herd experiences multiple does with profuse watery diarrhea, weight loss, and bottle jaw (submandibular edema) over several months. Fecal egg counts reveal heavy Haemonchus contortus burdens. Which anthelmintic resistance testing method is most appropriate to guide drug selection?
- Baermann technique to detect larvae in feces
- Fecal Egg Count Reduction Test (FECRT) comparing pre- and post-treatment counts (Correct answer)
- McMaster flotation to identify the species causing disease
- Larval development assay using pooled fecal cultures
Correct answer: Fecal Egg Count Reduction Test (FECRT) comparing pre- and post-treatment counts
The Fecal Egg Count Reduction Test (FECRT) is the gold-standard field test for anthelmintic resistance. Fecal egg counts are performed before and 14 days after treatment; <95% reduction indicates resistance. The Baermann technique detects lungworm larvae, not strongyles. McMaster identifies eggs but not resistance status.
Question 6: Scrapie is a prion disease of sheep. Which characteristic most accurately describes the diagnostic approach in suspect live animals?
- Serum ELISA for PrPSc antibodies
- PCR of blood for scrapie prion RNA
- Immunohistochemistry of lymphoid tissue (rectal biopsy or third eyelid) for PrPSc accumulation (Correct answer)
- Cerebrospinal fluid analysis showing 14-3-3 protein elevation
Correct answer: Immunohistochemistry of lymphoid tissue (rectal biopsy or third eyelid) for PrPSc accumulation
PrPSc (misfolded prion protein) accumulates in lymphoid tissues before neurologic signs appear. Immunohistochemistry (IHC) of rectal mucosa lymphoid tissue or the third eyelid can detect PrPSc antemortem in live sheep. There are no antibodies to prions (immune tolerance), and prions have no nucleic acid, making serology and PCR impossible.
NAVLE Small Ruminant Medicine (Sheep and Goats)
A 3-year-old dairy goat presents with progressive weight loss, decreased milk production, and bilateral carpal swelling.
Lung auscultation reveals diffuse crackles.
Cerebrospinal fluid analysis shows mononuclear pleocytosis.
The most likely diagnosis is: