NAVLE Bovine Herd Health 2 — Questions and Answers
Question 1: A beef cow herd has a 15% prevalence of Bovine Respiratory Disease (BRD) in newly arrived feedlot calves. Which metaphylactic antibiotic is most commonly used at arrival processing?
- Tulathromycin (Correct answer)
- Penicillin G
- Sulfadimethoxine
- Ampicillin
Correct answer: Tulathromycin
Tulathromycin (Draxxin) is a macrolide widely used for metaphylaxis in high-risk beef cattle due to its long tissue half-life and single-dose efficacy.
Question 2: Pinkeye (Infectious Bovine Keratoconjunctivitis) in a cow herd is most commonly caused by which organism?
- Moraxella bovis (Correct answer)
- Pasteurella multocida
- Mycoplasma bovis
- Listeria monocytogenes
Correct answer: Moraxella bovis
Moraxella bovis is the primary causative agent of IBK, producing a pilus that allows corneal attachment and a hemolysin that damages corneal epithelium.
Question 3: A dairy herd has an elevated somatic cell count (SCC) averaging 500,000 cells/mL. What SCC threshold is used by the USDA as the legal limit for Grade A milk in the US?
- 750,000 cells/mL (Correct answer)
- 400,000 cells/mL
- 1,000,000 cells/mL
- 250,000 cells/mL
Correct answer: 750,000 cells/mL
The US legal limit for bulk tank SCC in Grade A milk is 750,000 cells/mL, though the EU standard is stricter at 400,000 cells/mL.
Question 4: Which vaccination protocol is most effective for preventing Bovine Virus Diarrhea (BVD) in a cow-calf operation?
- Modified live BVD vaccine given before breeding (Correct answer)
- Killed BVD vaccine given at weaning only
- Modified live BVD vaccine given at parturition
- Killed BVD vaccine given in the third trimester
Correct answer: Modified live BVD vaccine given before breeding
MLV BVD vaccines given pre-breeding provide superior mucosal immunity and prevent fetal infection that leads to persistently infected (PI) calves.
Question 5: A rancher reports abortions in 8% of his beef cows in the last trimester. Brucella abortus is confirmed. Which test is used for the official US brucellosis eradication program to test individual cattle?
- Card test (Rose Bengal plate test) (Correct answer)
- ELISA only
- Complement fixation test
- PCR of milk
Correct answer: Card test (Rose Bengal plate test)
The card (Rose Bengal) test is the approved screening test in the US brucellosis eradication program, with positive reactors confirmed by the buffered acidified plate antigen (BAPA) or fluorescent polarization assay.
Question 6: Grass tetany (hypomagnesemic tetany) in beef cattle grazing lush spring pastures is best prevented by supplementing which mineral?
- Magnesium oxide in mineral mix (Correct answer)
- Calcium carbonate in water
- Sodium bicarbonate free-choice
- Zinc sulfate boluses
Correct answer: Magnesium oxide in mineral mix
Grass tetany results from hypomagnesemia; magnesium oxide in a palatable mineral mix is the standard prevention because magnesium has no adequate body reserve.
Question 7: In a feedlot outbreak of thromboembolism (liver abscesses leading to caudal vena cava thrombosis), which organism is most commonly isolated from liver abscesses in cattle?
- Fusobacterium necrophorum (Correct answer)
- Trueperella pyogenes
- Bacteroides melaninogenicus
- Clostridium perfringens
Correct answer: Fusobacterium necrophorum
Fusobacterium necrophorum is the primary pathogen in bovine liver abscesses, originating from rumenitis caused by high-concentrate diets.
NAVLE Bovine Herd Health 2
A beef cow herd has a 15% prevalence of Bovine Respiratory Disease (BRD) in newly arrived feedlot calves.
Which metaphylactic antibiotic is most commonly used at arrival processing?