NAVLE Bovine Herd Health 6

Question 1

A 450-cow dairy herd has a rolling herd average of 28,000 lbs milk/cow/year but a 21-day pregnancy rate of only 12%. The reproductive technician reports a first-service conception rate of 38%. Which metric most accurately identifies the PRIMARY bottleneck limiting reproductive efficiency in this herd?

Accepted Answer

21-day submission rate is likely below 60%, reducing the pregnancy rate independent of conception rate

Answer

The 21-day pregnancy rate (PR) = submission rate × conception rate. With a 38% conception rate, achieving a 21-day PR of 18–22% (industry target) requires a submission rate of ~47–58%. A 12% PR with 38% CR implies a submission rate of only ~32%, meaning fewer than one-third of eligible cows are being detected in estrus or enrolled in a timed-AI protocol every 21 days. The conception rate itself is acceptable; the failure to get cows submitted is the primary bottleneck. Addressing detection of estrus or expanding synchronization protocols would have the greatest impact.

Question 2

An 800-cow beef cow-calf operation has experienced a 14% calf loss from birth to weaning over the past two years. Post-mortem findings in calves under 3 days old predominantly show fibrinous peritonitis and omphalophlebitis. In calves 3–21 days old, findings are predominantly abomasal bloat and villous atrophy. Which integrated management change addresses BOTH age-specific mortality peaks simultaneously?

Accepted Answer

Implement a Sandhills Calving System and vaccinate cows pre-partum with a multivalent scours vaccine containing K99 E. coli, rotavirus, coronavirus, and Clostridium perfringens C&D

Answer

The neonatal deaths (<3 days) with omphalophlebitis and peritonitis suggest failure of passive transfer combined with environmental contamination (navel infection), consistent with high pathogen load in the calving area. Deaths at 3–21 days with villous atrophy point to enteric viral pathogens (rotavirus/coronavirus). The Sandhills Calving System (moving cow-calf pairs away from the calving area as calves age) dramatically reduces pathogen build-up, addressing early-neonatal infection risk. Pre-partum cow vaccination with a multivalent scours vaccine boosts colostral antibodies against the enteric pathogens responsible for the later peak. The combination targets both windows of loss synergistically.

Question 3

A 1,200-head Holstein dairy uses a voluntary waiting period (VWP) of 50 days. Herd records show mean days to first service = 58 days, mean days open = 145 days, and 12-month rolling culling rate = 32%. The herd veterinarian proposes shortening the VWP to 35 days. Which of the following accurately predicts the PRIMARY unintended consequence of this change in a high-producing herd averaging 95 lbs/cow/day at peak?

Accepted Answer

First-service conception rate will decline because insemination will more frequently occur before complete uterine involution and during peak negative energy balance

Answer

In high-producing dairy cows, the nadir of negative energy balance (NEB) typically occurs between 10–14 days in milk, but NEB persists and substantially impairs reproductive function through ~50–60 DIM. Shortening the VWP to 35 days means many cows will be inseminated while still in NEB, with incomplete uterine involution, suboptimal progesterone profiles, and impaired embryo survival. Research consistently shows that conception rates at early first service in high-producers are 8–15 percentage points lower than services at 50–60 DIM. Additionally, uterine involution is not complete in many cows before 40–45 DIM. The net result is more services per conception and no improvement in days open, negating the intended benefit.

Question 4

During a herd health visit to a 600-cow feedlot, you identify a pen of 150 steers (day 14 on feed) with a 9% morbidity rate. Pulled animals show biphasic fever, nasal discharge, and decreased rumination. At necropsy of a non-responder, you find cranioventral pulmonary consolidation, fibrinous pleuritis, and isolation of Mannheimia haemolytica serotype 1. The owner's current protocol uses metaphylaxis with tulathromycin on arrival. Which finding is MOST consistent with a failure of metaphylactic protocol rather than a true treatment failure?

Accepted Answer

The majority of morbidity cases are occurring between days 10–21 post-arrival, suggesting the 96-hour effective plasma concentration window of tulathromycin was exceeded before challenge

Answer

Tulathromycin achieves concentrations above the MIC for M. haemolytica in lung tissue for approximately 96 hours (4 days) post-injection, though tissue concentrations remain elevated longer. However, protection against clinical BRD is generally considered most effective for the first 10–14 days post-treatment. Morbidity clustering at days 10–21 indicates the window of metaphylactic protection has passed before the peak of viral/bacterial challenge — a pharmacokinetic/epidemiological timing mismatch. M. haemolytica serotype 1 retains susceptibility to macrolides including tulathromycin in most North American feedlot populations. Fibrinous pleuritis in a necropsy animal likely reflects disease progression in that individual, not herd-wide chronicity. A 9% rate in a high-risk pen is above acceptable thresholds (typically <5–8% depending on risk classification).

Question 5

A closed beef herd of 300 Angus cows has had three consecutive years of late-gestation abortions (>7 months), averaging 4.5% abortion rate. Aborted fetuses show autolysis. Paired serology on 15 aborting cows shows no significant titer rise to IBR, BVD, leptospirosis (5-serovar panel), or Neospora caninum. Fetal abomasal content culture is negative. The pastures border a large white-tailed deer population. Which diagnostic step has the HIGHEST probability of identifying the etiology?

Accepted Answer

Submit fresh and formalin-fixed fetal tissues for PCR and histopathology targeting Epizootic Hemorrhagic Disease virus (EHD) and Bluetongue virus

Answer

The epidemiologic profile — late-gestation abortions, proximity to white-tailed deer (the primary amplifying host), and negative results for common abortifacients — strongly implicates an Orbivirus. EHD virus (serotypes 1, 2, 6, 7) and Bluetongue virus are transmitted by Culicoides midges, are amplified in deer populations, and can cause late-term abortion, fetal edema, and hemorrhage in cattle — often with autolytic fetuses making serology the only ante-mortem option in the dam. Importantly, EHD is frequently under-diagnosed because standard bovine abortion panels do not routinely include it. PCR on fresh fetal spleen, lung, and brain, combined with histopathology showing fetal vasculitis, would be confirmatory. Brucellosis is a legitimate consideration but would be unusual in a closed, vaccinated herd with no travel history and is mandatorily reportable, making it higher-profile. BVDV-PI cattle cause early losses, not clustering in late gestation.

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE Bovine Herd Health 6