NAVLE Bovine Herd Health 3 — Questions and Answers
Question 1: A dairy herd manager asks about dry cow therapy. Which approach describes selective dry cow therapy (SDCT)?
- Treating only cows with elevated SCC or positive culture at dry-off (Correct answer)
- Treating all cows with intramammary antibiotics at dry-off
- Treating only fresh cows showing clinical mastitis
- Withholding all treatment during the dry period
Correct answer: Treating only cows with elevated SCC or positive culture at dry-off
Selective dry cow therapy targets only cows with evidence of intramammary infection, reducing antibiotic use compared to blanket dry cow therapy.
Question 2: Calf scours causing the highest mortality in calves under 5 days of age on a US beef operation is most commonly caused by which pathogen?
- Escherichia coli (enterotoxigenic) (Correct answer)
- Cryptosporidium parvum
- Rotavirus
- Salmonella typhimurium
Correct answer: Escherichia coli (enterotoxigenic)
Enterotoxigenic E. coli (K99 fimbriae, F5 antigen) causes profuse watery diarrhea and rapid death in calves under 4 days old due to severe dehydration.
Question 3: A producer wants to reduce the risk of hardware disease (traumatic reticuloperitonitis) in his dairy herd. What is the most cost-effective preventive measure?
- Administering rumen magnets to all cows (Correct answer)
- Installing metal detectors on TMR feeders only
- Feeding chopped hay to slow rumen contractions
- Vaccinating with Clostridium perfringens toxoid
Correct answer: Administering rumen magnets to all cows
A permanent ceramic or bar magnet placed in the reticulum captures ingested ferrous metal objects, preventing them from penetrating the reticulum wall.
Question 4: Which internal parasite is responsible for 'ostertagiosis type II' (winter ostertagiosis) causing severe hypoproteinemia and diarrhea in yearling cattle?
- Ostertagia ostertagi (Correct answer)
- Haemonchus placei
- Cooperia oncophora
- Oesophagostomum radiatum
Correct answer: Ostertagia ostertagi
Type II ostertagiosis occurs when inhibited L4 Ostertagia ostertagi larvae resume development in late winter/spring, massively emerging from gastric glands and causing profound hypoproteinemia.
Question 5: A beef operation loses 3 cows to sudden death with no premonitory signs. Necropsy reveals a 'paint-brush' hemorrhage pattern on the heart and rapid bloat. Which clostridial disease is most likely?
- Blackleg (Clostridium chauvoei) (Correct answer)
- Black disease (Clostridium novyi type B)
- Enterotoxemia type D (Clostridium perfringens)
- Malignant edema (Clostridium septicum)
Correct answer: Blackleg (Clostridium chauvoei)
Blackleg (C. chauvoei) classically affects young cattle 6–24 months, causing myonecrosis with rapid death and characteristic crepitant swellings and myocardial hemorrhage.
Question 6: On a 500-cow dairy, the conception rate to first service drops from 42% to 28% over 3 months. Which herd-level factor should be investigated first?
- Heat detection efficiency and estrus expression (Correct answer)
- Bull fertility in the herd sire
- BVD vaccination status of heifers only
- Milk production records from 6 months ago
Correct answer: Heat detection efficiency and estrus expression
In AI-based dairies, poor heat detection is the most common cause of declining first-service conception rates, as undetected or wrongly timed AI submissions drive down the metric.
Question 7: What is the recommended colostrum management '1-2-3 rule' for newborn dairy calves?
- 1 gallon within 2 hours of birth, immunoglobulin concentration ≥50 g/L (Brix ≥22%) (Correct answer)
- 1 pint within 3 hours, tested by refractometer at ≥30% Brix
- 2 liters within 1 hour, IgG ≥22 g/L confirmed by colostrometer
- 3 feedings within the first day, 1 liter each time
Correct answer: 1 gallon within 2 hours of birth, immunoglobulin concentration ≥50 g/L (Brix ≥22%)
The 1-2-3 rule recommends 1 gallon (≈4 L) of high-quality colostrum (≥50 g/L IgG) fed within the first 2 hours after birth, with a Brix refractometer reading ≥22% confirming adequate quality.
NAVLE Bovine Herd Health 3
A dairy herd manager asks about dry cow therapy.
Which approach describes selective dry cow therapy (SDCT)?