NAVLE Bovine Herd Health Management 4

Question 1

A 400-cow dairy herd has a 21-day pregnancy rate of 12% despite adequate submission rates. Progesterone assays on Day 7 post-insemination show adequate luteal function in 85% of cows. Uterine cytology at Day 14 post-calving reveals >18% polymorphonuclear cells (PMNs) in 35% of cows. Which intervention is MOST likely to improve the 21-day pregnancy rate in this herd?

Accepted Answer

Add a presynchronization protocol (Presynch-Ovsynch) before initiating timed AI

Answer

With adequate luteal function but low 21-day pregnancy rate, the bottleneck is likely poor synchrony and ovulation at the time of AI rather than progesterone insufficiency. Presynchronization (Presynch-Ovsynch) improves follicular wave synchrony before the Ovsynch protocol, increasing the proportion of cows that respond with a dominant follicle and ovulate at timed AI — consistently shown to raise pregnancy per AI by 5–10 percentage points. Blanket cephapirin infusion is not recommended due to antimicrobial stewardship concerns and no proven efficacy for subclinical endometritis at 7 days. GnRH at AI addresses ovulation failure but does not address poor synchronization upstream. Extending the VWP would reduce submission rate, worsening the 21-day pregnancy rate.

Question 2

During a herd health visit to a 600-head beef cow-calf operation, you identify an outbreak of respiratory disease in calves 3–8 weeks of age. Morbidity is 28% and case-fatality rate is 9%. Nasal swabs from 6 acutely affected calves yield Mannheimia haemolytica in 4 and Histophilus somni in 2. Colostrum management records are excellent. Which pathogen-level finding MOST strongly suggests a vaccine-preventable gap in this herd's prevention program?

Accepted Answer

Bovine respiratory syncytial virus (BRSV) antigen detected on immunofluorescence of nasal swabs

Answer

BRSV is a primary viral pathogen in young calves that acts as a 'door-opener' for secondary bacterial pneumonia by disrupting mucociliary clearance and innate immunity. Its presence in calves this age with high morbidity despite good colostrum transfer points directly to a gap in dam vaccination (modified-live BRSV given pre-calving provides colostral antibody protection) or to inadequate calf vaccination timing. Mannheimia and Histophilus are secondary bacterial opportunists commonly cultured from BRD cases regardless of vaccination status. Pasteurella multocida type A treatment failure most suggests antimicrobial resistance or inadequate drug selection, not a specific vaccine gap.

Question 3

A 1,200-head commercial feedlot is experiencing an increased rate of liver condemnations at slaughter (18% vs. the target <10%). Rumen pH monitoring via rumenocentesis on 12 randomly selected cattle 6 hours post-feeding shows a mean rumen pH of 5.8 with 4 animals below 5.5. The current ration uses dry-rolled corn at 85% of dry matter. Which management change will MOST directly address the primary pathophysiological mechanism driving the liver condemnation rate?

Accepted Answer

Add monensin at 200–360 mg/head/day to shift ruminal fermentation toward propionate

Answer

Liver abscesses (the primary cause of liver condemnations in feedlots) result from rumenitis → rumen wall ulceration → bacteremia with Fusobacterium necrophorum seeding the liver. Subacute rumen acidosis (SARA, pH 5.5–5.8) is the driver of rumenitis. Monensin, an ionophore, shifts fermentation away from butyrate/propionate ratios that damage the rumen epithelium, reduces lactic acid accumulation, and directly reduces liver abscess rates by ~50% — the most validated single intervention. High-moisture corn actually ferments more rapidly than dry-rolled corn, potentially worsening acidosis. Increasing roughage helps buffer pH but is less targeted and reduces energy density. Virginiamycin specifically targets acute lactic acidosis (Streptococcus bovis/Lactobacillus), which is not the predominant concern here given pH values in the SARA range rather than <5.0.

Question 4

You are consulting on a biosecurity plan for a seedstock beef operation importing 15 breeding bulls from three different sources. Johne's disease (paratuberculosis) is a primary concern. Which combination of testing and quarantine procedures reflects current AAVLD/USAHA Voluntary Johne's Disease Herd Status Program (VJDHSP) Tier 3 recommendations for incoming animals?

Accepted Answer

Two negative fecal PCR tests 30 days apart during a 60-day quarantine before introduction

Answer

Under the VJDHSP framework, bulls entering a Tier 3 or higher herd should ideally have two negative high-sensitivity fecal tests (PCR or culture) performed at least 30 days apart during a quarantine period of at least 60 days. Fecal PCR has largely supplanted fecal culture as the preferred diagnostic due to faster turnaround and comparable sensitivity in intermittent shedders. A single serum ELISA has poor sensitivity in subclinical animals (50–60%) and is insufficient alone. Pooled samples reduce sensitivity further and are inappropriate for individual animal clearance. A 14-day quarantine is insufficient to detect intermittent shedders and does not meet Tier 3 biosecurity standards.

Question 5

A 350-cow dairy in the upper Midwest has a bulk tank somatic cell count (BTSCC) persistently between 320,000–380,000 cells/mL over the past 6 months. Milk culture of individual quarter samples from 40 randomly selected cows identifies: Staphylococcus aureus (6 cows), Streptococcus agalactiae (12 cows), coagulase-negative staphylococci (CNS) (8 cows), and no growth (14 cows). Which statement BEST describes the appropriate herd-level eradication target for this situation?

Accepted Answer

Streptococcus agalactiae should be targeted for herd eradication because it is an obligate intramammary pathogen that can be eliminated with a blitz dry-cow therapy program

Answer

Streptococcus agalactiae is an obligate pathogen of the bovine mammary gland — it does not survive long in the environment — making it the only major mastitis pathogen amenable to true herd eradication. A 'blitz' program (treating all infected cows simultaneously with intramammary penicillin + stringent milking hygiene + test and cull if refractory) can eliminate S. agalactiae from a herd within weeks. With 12/40 cows infected (30%), this organism is almost certainly the dominant driver of the elevated BTSCC. S. aureus has very poor cure rates with lactating cow therapy (<25%) and is not eradicable herd-wide. CNS generally cause mild, self-limiting IMI and rarely require active treatment. Blanket intramammary pirlimycin for all positive cows is not evidence-based and raises antimicrobial stewardship concerns.

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE Bovine Herd Health Management 4