NAVLE Bovine Herd Health 4 — Questions and Answers
Question 1: A herd of stocker cattle develops red-water disease (bacillary hemoglobinuria). Which organism and predisposing factor is responsible?
- Clostridium haemolyticum, liver fluke migration (Correct answer)
- Clostridium novyi type A, wound contamination
- Clostridium perfringens type C, high-grain diet
- Clostridium septicum, skin wounds in wet conditions
Correct answer: Clostridium haemolyticum, liver fluke migration
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?
- Ergovaline (Correct answer)
- Zearalenone
- Deoxynivalenol
- Fumonisin B1
Correct answer: Ergovaline
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?
- Serum beta-hydroxybutyrate (BHB) ≥1.2 mmol/L (Correct answer)
- Blood glucose <2.5 mmol/L
- Serum NEFA >0.4 mEq/L at dry-off only
- Urine acetone dipstick color change
Correct answer: Serum beta-hydroxybutyrate (BHB) ≥1.2 mmol/L
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?
- Dermacentor andersoni and Dermacentor variabilis ticks (Correct answer)
- Aedes aegypti mosquitoes
- Haematobia irritans horn flies
- Stomoxys calcitrans stable flies
Correct answer: Dermacentor andersoni and Dermacentor variabilis ticks
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?
- Anagyrine (quinolizidine alkaloid in lupine) (Correct answer)
- Swainsonine (locoweed)
- Veratrum californicum alkaloids
- Nitrates from sudan grass
Correct answer: Anagyrine (quinolizidine alkaloid in lupine)
Anagyrine in lupine species causes crooked calf disease (arthrogryposis and cleft palate) when dams graze lupine between days 40 and 70 of gestation.
Question 6: When calculating the economic impact of mastitis in a dairy herd, which production loss component is typically the largest?
- Reduced milk production (discarded milk + production drop) (Correct answer)
- Antibiotic treatment costs
- Veterinary labor and diagnostic fees
- Premature culling costs
Correct answer: Reduced milk production (discarded milk + production drop)
Reduced milk yield accounts for approximately 60–70% of total mastitis costs; clinical and subclinical cases each cow produces significantly less milk throughout the lactation.
Question 7: A veterinarian is conducting a pre-breeding soundness exam (BSE) on a herd bull. According to the Society for Theriogenology minimum standards, what minimum total motility percentage is required for a 'satisfactory' classification?
- 30% progressively motile sperm (Correct answer)
- 50% total motility
- 60% morphologically normal sperm
- 25% progressive motility with normal morphology >70%
Correct answer: 30% progressively motile sperm
The SFT BSE minimum requires ≥30% progressively motile sperm and ≥70% morphologically normal sperm for a satisfactory potential breeder classification.
NAVLE Bovine Herd Health 4
A herd of stocker cattle develops red-water disease (bacillary hemoglobinuria).
Which organism and predisposing factor is responsible?