NAVLE Bovine Herd Health Management 6

Question 1

A beef cow herd experiences a cluster of late-term abortions (7–9 months gestation) over 3 weeks. Fetuses show autolysis with placentitis. Serologic titers for Neospora caninum are elevated in affected cows but not in non-aborted herdmates. Which epidemiologic pattern best supports transient epidemic neosporosis rather than endemic neosporosis in this herd?

Accepted Answer

Abortions are concentrated in first-calf heifers and 2-year-olds with a rapid onset and high attack rate, while older cows are largely spared

Answer

Epidemic (point-source) neosporosis typically results from a sudden environmental exposure—such as contamination of feed or water with dog feces containing Neospora oocysts. This produces a high attack rate concentrated in a short time window and often disproportionately affects naive younger animals that lack any prior immunity. Endemic neosporosis, by contrast, is maintained by vertical (transplacental) transmission and tends to show a steady low-level abortion rate (1–3%) distributed across all age groups with seropositive dams producing seropositive offspring over successive years.

Question 2

A 450-cow dairy herd has a bulk tank somatic cell count (BTSCC) persistently between 350,000–420,000 cells/mL despite standard mastitis control measures. Pathogen culture of composite milk from cows with SCC >200,000 cells/mL reveals 68% Streptococcus agalactiae. Which intervention would most rapidly reduce the BTSCC in this contagious mastitis scenario?

Accepted Answer

Initiate blitz therapy: treat all culture-positive cows simultaneously with intramammary penicillin while they remain in the milking herd

Answer

Streptococcus agalactiae is an obligate intramammary pathogen exquisitely sensitive to penicillin. Blitz therapy—treating all infected cows simultaneously with intramammary penicillin (with or without systemic support) while they remain in the milking string—achieves rapid, herd-level cure rates exceeding 90% and can dramatically reduce BTSCC within a single lactation. Selective dry cow therapy is effective for long-term control but does not treat cows currently in lactation. Segregation and milking-last slow transmission but do not cure existing infections. Improved teat disinfection addresses environmental or contagious spread prevention but does not eliminate existing infections.

Question 3

During a herd health visit to a 600-cow commercial beef operation, you identify a 4% prevalence of footrot (Fusobacterium necrophorum / Trueperella pyogenes) over the past 60 days despite routine zinc sulfate footbathing. Environmental assessment reveals persistently saturated soil near the water tanks. The producer asks about strategic use of long-acting oxytetracycline (LA-OTC) as a herd-level preventive. Under which circumstance is this practice MOST appropriately justified?

Accepted Answer

As a targeted 3–5 day pulse administered to at-risk groups when known high-risk periods (e.g., prolonged wet season) cannot be mitigated environmentally

Answer

Strategic pulse use of LA-OTC during defined high-risk periods—when wet, muddy conditions cannot be corrected—is the most defensible application of antimicrobial prevention for footrot. It limits antimicrobial use to temporally justified windows, reducing selection pressure. Mass medication as a routine monthly program regardless of risk violates antimicrobial stewardship principles. Replacing footbathing entirely with antimicrobials is not appropriate because environmental management is the cornerstone of prevention. Twice-weekly injections represent inappropriate use frequency and dosing regimen for preventive purposes and are inconsistent with any approved label indication.

Question 4

A 320-cow spring-calving beef herd experiences a 22% calf scours rate in calves aged 3–10 days, with 6 deaths. ELISA fecal antigen testing of 12 affected calves yields: Cryptosporidium parvum positive in 10/12, rotavirus positive in 5/12, and coronavirus positive in 2/12. Bulk colostrum Brix refractometer readings average 18%. Which management interpretation is MOST accurate?

Accepted Answer

Colostrum quality is acceptable; the outbreak is driven by environmental pathogen pressure from a calving area that has exceeded its safe carrying capacity

Answer

A Brix reading of ≥22% is the standard threshold for high-quality bovine colostrum (correlating with IgG ≥50 g/L). At 18% average Brix, colostrum quality is actually borderline-to-acceptable (most thresholds are ≥21–22% for 'excellent'), but notably the dominant pathogen is Cryptosporidium parvum—which is NOT prevented by colostrum-derived antibodies in any meaningful clinical sense because C. parvum pathogenesis occurs intraluminally and FPT does not specifically predispose to cryptosporidiosis. The 10/12 prevalence of C. parvum with calves 3–10 days old is the classic epidemiologic signature of environmental fecal-oral contamination pressure, typically amplified by overcrowding, reuse of calving areas, and accumulation of oocysts in the environment (the 'herd effect' or Ames Iowa model). The calving area has almost certainly exceeded its safe pathogen load. While colostrum quality should still be optimized, the outbreak driver here is environmental pressure, not FPT.

Question 5

A 900-cow Holstein dairy herd participates in a reproductive program using GnRH-based synchronization (Ovsynch). Despite high estrus synchronization compliance, 21-day pregnancy rates have plateaued at 18%. Detailed records show: AI submission rate 92%, conception rate (CR) 21%, pregnancy loss 12% (day 28–56). The reproductive specialist suspects subclinical endometritis. Which diagnostic criterion BEST defines subclinical endometritis in lactating dairy cows, and what is the recommended threshold for treatment intervention in this herd?

Accepted Answer

Uterine cytology showing ≥8% PMNs (≥35–47 days postpartum) or ≥18% PMNs (≥20–33 days postpartum); treat cows above threshold with intrauterine cefapirin

Answer

Subclinical endometritis (SCE) is definitively diagnosed by uterine cytology (cytobrush or lavage) rather than visual discharge scoring. The validated thresholds differ by postpartum timing: ≥18% PMNs at 20–33 DIM and ≥8% PMNs at 34–47 DIM, reflecting the physiological decline in uterine PMNs as the postpartum period progresses. Intrauterine cefapirin (a first-generation cephalosporin with broad uterine penetration and no systemic withdrawal concerns) is the most evidence-supported treatment for SCE. Vaginoscopy and Metricheck detect clinical endometritis/metritis but miss subclinical disease by definition. Systemic ceftiofur is used for acute puerperal metritis, not SCE. Uterine diameter by palpation does not reliably diagnose SCE.

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE Bovine Herd Health Management 6