John Kirk, DVM, MPVM
Veterinary Medicine Extension
UC Davis, Tulare

Have you had a recent visit from your drug salesman and been told that their BVD vaccine is better than others because it stimulates a higher titer or contains Type II virus? Are you confused? A recent article in Large Animal Practice (21:1 14-17, 2000) may give you a new perspective on BVD vaccines.

Can modified live BVD vaccines be used in suckling calves without causing illness in their dams? It is possible but not probable that BVD infection might spread from the calves. Replication in the nose of the vaccinated calf is a highly inefficient means of transmitting disease. What little BVD virus that might get transferred will surely be not survive in a immunocompetent (ie vaccinated) dam.

Do BVD vaccine titers indicate whether the animal is protected or not? Keep in mind that titers are often used by sale people to sell their product or belittle another product. A single dose of a MLV Type 1 vaccine will protection to even young calves from severe clinical disease even with exposure to Type 2 BVD. Inactivated BVD vaccines when properly administered (following the manufacture's recommendations) will achieve the same effect. However, it will take longer to develop protective immunity as they required a second or booster dose. All this can happen without the detection of but minimal titers. Why is this possible? Because the vaccines when properly used will allow the animals to react more quickly with its own immune system after BVD challenge rather than preventing infection.

Why do most BVD infections or outbreaks take place? Simple, lack of vaccination. Either no vaccination or failure to follow the manufactures recommendations.

Do BVD vaccines protect equally against all the different forms of BVD? No. When properly administered, BVD vaccines do a very good job in preventing serious outbreaks of clinical disease such as diarrhea. However, they may not prevent all problems for the fetus. When exposed, a BVD vaccinated cow will be protected from clinical disease, but a small amount of virus may pass the placenta and infected the fetus. As only a small amount of virus is necessary to harm the fetus, a resorption or abortion may result from even very minimal exposure. Perhaps that is why no current vaccines claim to give fetal protection. BVD vaccines are about 80% efficacious in protecting the fetus.

No vaccine is 100% effective or totally safe. It is a matter of what risk the dairymen is willing to take. The fact still remains that unprotected animals are at very high risk while vaccinated animals are at low risk from BVD virus. So dairymen should continue to vaccinate for BVD realizing these limitations.