by Melissa Goldade

The recent outbreak of BVD in Wisconsin has many producers wondering what they can do to prevent infections in their herds. According to Dr. Ron Schultz from the University of Wisconsin School of Veterinary Science in Madison, vaccination is a big key in prevention.

"It is not clear whether this is a new strain of BVD or rather the combination of a different, more virulent strain being introduced to cattle that have not been part of a thorough vaccination program," says Dr. Schultz.

New animals are big factor
Most of the herds that have had outbreaks recently have a similar factor, they have introduced new animals into the herd. According to Dr. Schultz, the biggest cause of acute outbreaks is bringing in new animals to a herd that has not followed a structured vaccination program. This is especially true in herds that are expanding or that buy bred heifers.

"The problem is that you can't tell without screening if any of the animals are infected with BVD or are persistent carriers," says Dr. Schultz. "You are introducing the BVD virus to animals that have either not been vaccinated or exposed to that strain of BVD, and the result may be an acute outbreak with a high death loss."

If a herd has a persistent carrier of BVD, it will always show signs of subtle BVD as long as that animal is in the herd, regardless of the vaccination program. However, a good vaccination program will prevent acute outbreaks.

"The problem is that the persistent carrier of BVD does not show signs of being sick. She seems perfectly normal and healthy," says Dr. Schultz. "We have a 16 year old persistent carrier in our experimental herd that is one of the best cows in the herd. You can't just simply look at an animal and know that it is a persistent carrier.

"If you have signs of BVD in your herd, you should screen all animals to find out which ones are carriers and these animals should be sent to slaughter immediately. This will help eliminate problems in your herd as well as for people who buy animals from you."

Carriers infected as fetuses
The problem in identify persistent carriers without screening is that they are infected as fetuses. When an infected animal is introduced to the herd, some fetuses in the first 100 days of gestation may become persistent carriers. However, if the dam has been on a thorough vaccination program, the fetus will also be protected from becoming infected.

Vaccination a key in prevention
"If a herd has followed a good and thorough vaccination program, we usually don't see acute outbreaks such as the recent ones in Wisconsin. However, if the program is spotty, incorrect vaccines are used, or the incorrect dosage is given, we tend to see more problems," continues Dr. Schultz.

Young animals, 6-15 months, should be given two doses modified live vaccine to insure a good immunity. Dr. Schultz recommends giving the first shot at six months and the second one at least 45 days before breeding. If you choose to use a killed vaccine, two doses should be given 2-3 weeks apart at six months old and two more doses before breeding.

Dr. Schultz recommends using the modified live vaccines, since they need only 10-14 days to take effect and they give better immunity. Killed vaccine takes a minimum of 4-6 weeks after the first dose to provide protection and the protection is generally not as complete as with a modified live vaccine. However, modified live cannot be used on pregnant animals, whereas killed may. Dr. Schultz warns that even killed vaccines used on pregnant animals may cause some problems in a small number of animals.

A good vaccination program consists of revaccinating at least once a year. It is important to keep up on shots with the youngstock also, being sure to vaccinate twice before breeding and then following through on a 12 month interval after freshening.

Dr. Schultz recommends working closely with your veterinarian to use current effective products and to insure that they are used properly. If you are planning to bring new animals into your herd, it is critical that you have a vaccination program in place. If you don't, consult your veterinarian prior to introducing the new animals since you'll want to be sure that your herd is properly vaccinated before the new animals arrive.