NAVLE Bovine Herd Health 4

Question 1

A herd of stocker cattle develops red-water disease (bacillary hemoglobinuria). Which organism and predisposing factor is responsible?

Accepted Answer

Clostridium haemolyticum, liver fluke migration

Answer

Bacillary hemoglobinuria is caused by C. haemolyticum (C. novyi type D), which proliferates in anaerobic zones created by migrating Fasciola hepatica liver flukes.

Question 2

Which reproductive toxin produced by endophyte-infected tall fescue grass causes 'summer slump' and reduced pregnancy rates in beef cows?

Accepted Answer

Ergovaline

Answer

Ergovaline from the Neotyphodium coenophialum endophyte causes vasoconstriction, hyperthermia, and poor reproductive performance in cattle grazing infected fescue.

Question 3

A dairy producer wants to monitor transition cow health. Which single blood test best predicts subclinical ketosis in fresh cows?

Accepted Answer

Serum beta-hydroxybutyrate (BHB) ≥1.2 mmol/L

Answer

Serum BHB ≥1.2 mmol/L (1.0–1.4 mmol/L threshold range) measured in the first 2 weeks postpartum is the gold standard for diagnosing subclinical ketosis.

Question 4

Anaplasmosis in cattle is transmitted primarily by which vector in the US?

Accepted Answer

Dermacentor andersoni and Dermacentor variabilis ticks

Answer

Anaplasma marginale is transmitted by Dermacentor tick species in the US, though mechanical transmission by biting flies and blood-contaminated instruments also occurs.

Question 5

A beef herd in the southeastern US has calves born with contracted tendons, cleft palate, and arthrogryposis. The dam grazed lupine between days 40–70 of gestation. Which teratogen is responsible?

Accepted Answer

Anagyrine (quinolizidine alkaloid in lupine)

Answer

Anagyrine in lupine species causes crooked calf disease (arthrogryposis and cleft palate) when dams graze lupine between days 40 and 70 of gestation.

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE Bovine Herd Health 4