AVMA ABVS-recognised specialty boards Food-Animal Production Medicine & Herd Health: practice questions

Question 1 · hard

A close-up dry cow ration contains, on a dry matter basis, 0.12% Na, 1.20% K, 0.80% Cl and 0.40% S. Using equivalent weights of 23, 39.1, 35.45 and 16, what is its DCAD, (Na + K) − (Cl + S), in mEq/kg DM?

1. About −116 mEq/kg DM
2. About −12 mEq/kg DM
3. About +133 mEq/kg DM
4. About +116 mEq/kg DM

Question 2 · hard

In early lactation Holstein cows, a herd shows milk fat-to-protein ratios above 1.5 in many cows in the first month. What does this most likely indicate?

1. Subacute ruminal acidosis from a ration with too little physically effective fibre
2. Protein excess in the diet causing high milk urea and a raised milk protein level
3. A new outbreak of contagious mastitis caused by Streptococcus agalactiae infection
4. Excessive body fat mobilisation from negative energy balance, and so a raised risk of ketosis

Question 3 · hard

A dairy herd's first-service conception rate has fallen from 42% to 28% during the hot season while submission rate is unchanged. Which explanation best fits?

1. Over-conditioned cows at drying off, which lowers conception only in the hot months
2. Heat stress reducing oocyte quality and early embryo survival, lowering conception
3. An outbreak of digital dermatitis, since lameness only lowers conception and not submission
4. A fall in heat detection, since heat stress mainly lowers the submission rate in cows

Question 4 · hard

A 40-kg calf is fed 4 L of colostrum containing 50 g/L IgG. At 24 hours its serum IgG is 20 g/L. Taking plasma volume as 9% of body weight, what is the apparent efficiency of absorption?

1. 40%
2. 36%
3. 10%
4. 72%

Question 5 · hard

Why are claw horn lesions such as sole ulcers more common in the first months after calving and in thin cows?

1. Thin cows grow horn faster than fat cows, so their soles become overgrown and ulcerate from excess thickness
2. Treponema bacteria multiply in the uterus after calving and then spread in the blood to the sole corium of the hind feet, where they cause ulcers
3. Hormonal loosening of the pedal bone's suspensory apparatus around calving and a thinner digital cushion let the pedal bone compress the corium
4. Calving raises the blood calcium level, which hardens the sole horn and cracks it in the first month after calving

Question 6 · hard

To be 95% confident of detecting at least one infected animal in a large herd if the true prevalence is 10%, using a perfect test, about how many animals must be sampled? Use n = ln(0.05) ÷ ln(1 − p).

1. 10
2. 59
3. 29
4. 95

Question 7 · hard

A herd tests 29 animals for a disease with a perfect test, designed to detect a 10% prevalence with 95% confidence, and all are negative. What conclusion is justified?

1. Prevalence is exactly 5%, because half the design prevalence is always the true value
2. The herd is proven completely free of the disease and can be certified as free for life
3. There is 95% confidence that prevalence is below 10%; freedom at lower prevalence is not shown
4. The test result is meaningless, because negative results never inform herd status

Question 8 · hard

A flock's FECRT shows reduced efficacy for two different anthelmintic classes. Which advice is most appropriate?

1. Stop all monitoring because resistance means no anthelmintic will ever work again
2. Double the dose of both failing classes for all animals in the flock and treat every three weeks through the grazing season
3. Rotate every class each month so that no worm is exposed to the same drug twice
4. Use an effective class confirmed by testing, preserve refugia, quarantine-treat bought stock and monitor egg counts

Question 9 · hard

Why does a timed AI programme alone often fail to raise the pregnancy rate in a herd with a high prevalence of subclinical endometritis?

1. It works only in heifers, because adult cows do not respond to GnRH at all
2. It raises submission but cannot overcome the low conception caused by the uterine disease
3. It cures the endometritis itself but delays insemination by one full oestrous cycle of 21 days
4. It lowers submission, since cows on the programme can no longer be seen in oestrus

Question 10 · hard

Why do many flock abortion investigations fail to reach a diagnosis?

1. Serology of the aborted ewes alone always identifies the causal agent more reliably than fetal tissues
2. Suitable fetuses and placentas are often not submitted fresh, and several agents need specific tests
3. All ovine abortion agents usually grow on routine culture within 24 hours, so negatives mean no cause
4. Abortion in sheep is always caused by nutrition, so laboratory testing finds nothing