NAVLE Bovine Herd Health Management 3 — Questions and Answers
Question 1: A dairy herd has a transition cow period disorder rate of 25% for clinical ketosis. Which nutritional management strategy is most effective at reducing periparturient ketosis?
- Feeding high-grain diet 6 weeks before calving
- Implementing a negative DCAD (Dietary Cation-Anion Difference) diet prepartum
- Feeding propylene glycol as a preventive drench in the close-up dry period (Correct answer)
- Increasing body condition score to 4.0 or higher at dry-off
Correct answer: Feeding propylene glycol as a preventive drench in the close-up dry period
Propylene glycol is a glucogenic precursor that, when drenched preventively in the close-up period or early postpartum, reduces the incidence of clinical ketosis by supporting hepatic gluconeogenesis.
Question 2: Which test is used to diagnose pregnancy toxemia (ketosis) in beef cows and can be performed on-farm using a handheld meter?
- Serum calcium measurement
- Blood beta-hydroxybutyrate (BHB) measurement (Correct answer)
- Packed cell volume (PCV)
- Serum total protein
Correct answer: Blood beta-hydroxybutyrate (BHB) measurement
Handheld ketone meters measuring blood beta-hydroxybutyrate (BHB) provide rapid on-farm diagnosis of subclinical and clinical ketosis, with subclinical ketosis defined as BHB ≥1.2 mmol/L.
Question 3: A beef producer reports that 20% of his cows are losing calves due to abortion in the second trimester. Fluorescent antibody testing of aborted fetal tissues confirms Neospora caninum. What is the most likely source of infection in this cow-calf herd?
- Contact with infected bulls during breeding
- Ingestion of feed or water contaminated with dog feces containing oocysts (Correct answer)
- Vertical transmission from infected cows to fetuses only
- Contact with infected deer at the fence line
Correct answer: Ingestion of feed or water contaminated with dog feces containing oocysts
Dogs are the definitive host for Neospora caninum and shed oocysts in feces; cattle are infected by ingesting contaminated feed or water, making canine fecal contamination the primary horizontal transmission route.
Question 4: What is the recommended minimum colostrum quality (Brix refractometer reading) indicating adequate IgG concentration for feeding to neonatal calves?
- ≥15% Brix
- ≥22% Brix (Correct answer)
- ≥10% Brix
- ≥30% Brix
Correct answer: ≥22% Brix
A Brix refractometer reading of ≥22% correlates with IgG concentrations ≥50 g/L, which is the threshold for high-quality colostrum suitable for feeding neonatal calves.
Question 5: A veterinarian is establishing a herd health program for a 500-cow dairy. Which parameter best defines 'failure of passive transfer' (FPT) in dairy calves?
- Serum IgG <10 g/L measured at 24-48 hours of age (Correct answer)
- Total serum protein <5.0 g/dL measured at 24-48 hours of age
- Serum IgG <10 g/L measured at 1-2 weeks of age
- Serum IgG <5 g/L measured within 6 hours of birth
Correct answer: Serum IgG <10 g/L measured at 24-48 hours of age
FPT is defined as serum IgG <10 g/L (or serum total protein <5.2 g/dL as a surrogate) measured at 24-48 hours of age, after the gut closes to macromolecular absorption.
Question 6: In a beef herd vaccination program, Bovine Viral Diarrhea Virus (BVDV) Type 1 and Type 2 vaccines are used. Which cattle are most critical to vaccinate to prevent persistently infected (PI) calves from being born?
- All bulls used for natural service
- Heifers and cows before breeding (Correct answer)
- Newborn calves in the first week of life
- Weaned calves at 6-8 months of age
Correct answer: Heifers and cows before breeding
PI calves result from fetal infection with BVDV between days 40-125 of gestation; vaccinating cows and heifers before breeding prevents viremia during this critical window.
Question 7: A producer observes stiff gait and muscle tremors in 2-week-old beef calves born to cows on selenium-deficient pastures. What is the most likely diagnosis?
- Polioencephalomalacia
- White muscle disease (nutritional muscular dystrophy) (Correct answer)
- Enterotoxemia (clostridial)
- Hypocalcemia (milk fever)
Correct answer: White muscle disease (nutritional muscular dystrophy)
White muscle disease (nutritional muscular dystrophy) is caused by selenium and/or vitamin E deficiency, presenting as muscle weakness, stiff gait, and tremors in young calves born in selenium-deficient areas.
NAVLE Bovine Herd Health Management 3
A dairy herd has a transition cow period disorder rate of 25% for clinical ketosis.
Which nutritional management strategy is most effective at reducing periparturient ketosis?