DVM Large Animal Medicine 5 — Questions and Answers
Question 1: A cow is treated with a prostaglandin F2α analogue to induce luteolysis. On which day of the estrous cycle will this treatment be MOST effective?
- Day 1-4 (early diestrus)
- Day 5-17 (mid to late diestrus) (Correct answer)
- Day 18-21 (late proestrus)
- Day 0 (estrus)
Correct answer: Day 5-17 (mid to late diestrus)
PGF2α is effective only when a functional corpus luteum is present (days 5-17 of the bovine estrous cycle); administration before day 5 or after day 17 will not induce luteolysis.
Question 2: Which of the following is the MOST important biosecurity measure to prevent introduction of bovine leukemia virus (BLV) into a naïve herd?
- Vaccination of all incoming cattle
- Testing and culling of BLV-positive animals before introduction (Correct answer)
- Mass anthelmintic treatment at arrival
- Quarantine for 30 days with respiratory monitoring only
Correct answer: Testing and culling of BLV-positive animals before introduction
BLV is transmitted via infected lymphocytes, so testing incoming cattle by ELISA or AGID and excluding seropositive animals is the most effective biosecurity measure.
Question 3: A horse is presented with acute laminitis following grain overload. Which underlying pathophysiologic mechanism is most directly responsible for lamellar disruption?
- Direct compression of the digital cushion by hoof wall
- Activation of matrix metalloproteinases degrading lamellar basement membrane (Correct answer)
- Immune complex deposition in the laminar vasculature
- Thrombosis of the digital arteries causing ischemic necrosis
Correct answer: Activation of matrix metalloproteinases degrading lamellar basement membrane
In laminitis, MMP activation (particularly MMP-2 and MMP-9) degrades the lamellar basement membrane, disrupting the bond between the sensitive and insensitive lamellae.
Question 4: Potomac horse fever is caused by which organism and transmitted by which vector?
- Ehrlichia equi transmitted by Ixodes ticks
- Neorickettsia risticii transmitted by ingestion of infected aquatic insects (Correct answer)
- Anaplasma phagocytophilum transmitted by Dermacentor ticks
- Theileria equi transmitted by Babesia-infected ticks
Correct answer: Neorickettsia risticii transmitted by ingestion of infected aquatic insects
Potomac horse fever is caused by Neorickettsia risticii, which infects aquatic flukes living in insects such as caddisflies; horses are infected by accidentally ingesting these insects near water.
Question 5: A feedlot steer develops peracute septicemia with hemorrhagic nasal discharge and dies within 24 hours. Post-mortem reveals hemorrhagic tracheitis and severe pulmonary edema. Which pathogen is most likely responsible?
- Mannheimia haemolytica
- Histophilus somni (thromboembolic meningoencephalitis) (Correct answer)
- Mycoplasma bovis
- Bovine herpesvirus-1 (IBR)
Correct answer: Histophilus somni (thromboembolic meningoencephalitis)
Histophilus somni can cause a peracute septicemic form with hemorrhagic tracheitis, myocarditis, and rapid death, in addition to the classic thromboembolic meningoencephalitis.
Question 6: A llama presents with a 2-week history of depression, anorexia, and progressive neurologic signs including ataxia and facial nerve paralysis. Listeria monocytogenes is suspected. Which antimicrobial is the drug of choice?
- Florfenicol
- Enrofloxacin
- Penicillin G at high doses (Correct answer)
- Tulathromycin
Correct answer: Penicillin G at high doses
High-dose penicillin G is the drug of choice for listeriosis in ruminants and camelids, as Listeria monocytogenes is reliably susceptible and penicillin penetrates the CNS adequately at high doses.
Question 7: Which of the following is the primary reason that NSAIDs (e.g., flunixin meglumine) are used in the treatment of endotoxemia in cattle, rather than solely for analgesia?
- They directly neutralize circulating lipopolysaccharide (LPS)
- They inhibit cyclooxygenase, reducing prostaglandin and thromboxane production triggered by endotoxin (Correct answer)
- They stimulate hepatic LPS clearance via Kupffer cells
- They block TNF-alpha receptor binding
Correct answer: They inhibit cyclooxygenase, reducing prostaglandin and thromboxane production triggered by endotoxin
Flunixin inhibits COX enzymes, reducing prostaglandin E2 and thromboxane A2 production that mediate the systemic inflammatory response to endotoxin, including fever, vasodilation, and coagulopathy.
