NAVLE Bovine Herd Health Management Questions and Answers — Questions and Answers
Question 1: A dairy manager reports a sudden increase in the herd's bulk tank somatic cell count (SCC). The majority of cows appear clinically normal. What is the most effective and practical initial step to identify the individual cows contributing to the high SCC?
- Culture a milk sample from the bulk tank to identify the causative pathogen.
- Immediately treat all lactating cows with a broad-spectrum intramammary antibiotic.
- Perform a California Mastitis Test (CMT) on milk from all lactating cows. (Correct answer)
- Cull all cows with a previous history of clinical mastitis.
Correct answer: Perform a California Mastitis Test (CMT) on milk from all lactating cows.
The California Mastitis Test (CMT) is a rapid, cow-side test that provides a semi-quantitative estimate of the SCC for individual cows (or quarters), allowing for the quick identification of animals with subclinical mastitis. While bulk tank culture identifies pathogens, it doesn't pinpoint the infected cows. Treating the whole herd is not cost-effective and is poor antimicrobial stewardship. Culling is a drastic measure used for chronically infected cows, not as an initial diagnostic step.
Question 2: Which of the following is the most critical control point for eliminating Bovine Viral Diarrhea Virus (BVDV) from a beef cow-calf herd?
- Vaccinating all adult animals annually with a modified-live virus (MLV) vaccine.
- Implementing a comprehensive fly and vector control program.
- Treating all clinically ill animals with supportive care and antibiotics.
- Identifying and removing persistently infected (PI) animals. (Correct answer)
Correct answer: Identifying and removing persistently infected (PI) animals.
Persistently infected (PI) animals are the primary reservoir and source of BVDV shedding within a herd. They become infected in utero and shed the virus throughout their lives. While vaccination is a key part of prevention, it may not be fully effective in the face of the massive viral load shed by a PI animal. Therefore, the most critical step for eradication is to test for, identify, and remove these PI animals from the population.
Question 3: A dairy producer utilizes a timed artificial insemination (TAI) protocol that includes Ovsynch. Which hormone is administered to cause luteolysis, or regression of the corpus luteum, thereby allowing the cow to return to estrus?
- Prostaglandin F2α (PGF2α) (Correct answer)
- Gonadotropin-releasing hormone (GnRH)
- Progesterone
- Oxytocin
Correct answer: Prostaglandin F2α (PGF2α)
Prostaglandin F2α (PGF2α) is the hormone responsible for causing luteolysis, which is the breakdown of the corpus luteum (CL). In synchronization protocols like Ovsynch, PGF2α is given when a mature CL is expected to be present, causing a drop in progesterone and allowing a new follicular wave to progress towards ovulation. GnRH is used to cause ovulation or start a new follicular wave, while progesterone (e.g., in a CIDR) is used to prevent estrus.
Question 4: Which dietary management strategy implemented during the final 2-3 weeks of the dry period is most effective for preventing periparturient hypocalcemia (milk fever) in dairy cows?
- Feeding a diet high in calcium to 'prime' the system.
- Supplementing with high levels of intravenous calcium.
- Feeding a diet with a negative Dietary Cation-Anion Difference (DCAD). (Correct answer)
- Maximizing dietary potassium to improve rumen function.
Correct answer: Feeding a diet with a negative Dietary Cation-Anion Difference (DCAD).
Feeding a diet with a negative Dietary Cation-Anion Difference (DCAD), also known as an acidogenic diet, is the most effective nutritional strategy to prevent milk fever. This diet induces a mild metabolic acidosis, which improves the cow's ability to mobilize calcium from bone and absorb it from the gut in response to parathyroid hormone (PTH) when the massive demand for calcium begins at calving. Feeding high calcium pre-calving or high potassium actually increases the risk of milk fever. IV calcium is a treatment, not a preventative feeding strategy.
Question 5: What is the most reliable and practical method for assessing failure of passive transfer (FPT) in a 2-day-old calf on-farm?
- Radial immunodiffusion (RID) assay
- Serum total protein measurement via refractometer (Correct answer)
- Visual assessment of calf vigor and suckle reflex
- Zinc sulfate turbidity test
Correct answer: Serum total protein measurement via refractometer
Measuring serum total protein (STP) with a refractometer is a widely used, practical, and reliable on-farm method to estimate passive immunity status. In neonatal calves, immunoglobulins (primarily IgG) make up a large portion of serum proteins, so there is a strong correlation between STP and serum IgG levels. While RID is the gold standard for directly measuring IgG, it is a laboratory test and not practical for immediate, on-farm assessment. Visual assessment is unreliable, and the zinc sulfate turbidity test is an older, less accurate method.
Question 6: A group of yearling beef cattle on pasture for the first time during late summer exhibit profuse watery diarrhea, poor growth, and submandibular edema ('bottle jaw'). Which of the following is the most likely diagnosis?
- Johne's Disease
- Coccidiosis
- Bovine Viral Diarrhea Virus (BVDV)
- Type I Ostertagiasis (Correct answer)
Correct answer: Type I Ostertagiasis
This clinical presentation is classic for Type I Ostertagiasis, caused by a heavy burden of the brown stomach worm, Ostertagia ostertagi. The parasites cause a protein-losing enteropathy, leading to hypoalbuminemia, which results in submandibular edema ('bottle jaw') and diarrhea. This typically affects young cattle in their first grazing season. Johne's disease typically affects older cattle, and while coccidiosis causes diarrhea, severe bottle jaw is less common.
NAVLE Bovine Herd Health Management Questions and Answers
A dairy manager reports a sudden increase in the herd's bulk tank somatic cell count (SCC).
The majority of cows appear clinically normal.
What is the most effective and practical initial step to identify the individual cows contributing to the high SCC?