BOVINE VIRUS DIARHEA: Part III

For the last two months we have been discussing the Bovine Virus Diarrhea Virus (BVDV) and the problems it causes for the beef cattle industry.  This applies to both the feedlot sector of the industry and to the cow/calf sector.  Now we need to discuss how we can prevent losses due to BVD and our current tools for prevention.

What are some important steps in preventing losses due to BVD?

The most important step is adoption of good management practices.  These are routine practices that aid in the prevention of all diseases in cattle, including BVD.  These include adequate nutrition as a cornerstone of prevention.  We must make sure that the cattle do not become too thin or too fat.  Both extreme conditions can decrease the ability of the animal’s immune response to fight infectious agents such as BVD.  In addition to general nutrition (adequate energy, protein, and clean water), some of the trace minerals can cause problems if in short supply.  Both selenium deficiency and copper deficiency are widespread in California beef cattle and will damage the immune system of deficient cattle.  Your veterinarian can take blood or tissue samples to determine the status of your cattle with respect to these trace minerals and recommend appropriate methods for supplementation.  The third item that is central to maintaining the resistance of cattle is the reduction of stress.  Stress commonly occurs during extremes in weather, handling, and transportation.  Methods to reduce stress will help the animals fight off infections of all types.  The final general item is the timing of preventive procedures such as vaccination.  From the time a vaccine is administered it takes at least 14 days for the initial immune response to occur.  Thus, if a group of cattle is vaccinated today for the first time and exposed to a field strain BVD virus two days from now, they are at least 12 days away from having a degree of protection.  In this example, the vaccine was not effective because of timing.

What type of BVD vaccine should I use?

There are two basic types of BVD virus vaccines.  Killed vaccines and Modified Live Virus (MLV) vaccines.  The killed vaccines contain large amounts of the killed BVD virus in a solution that helps to stimulate the immune response.  The MLV vaccines contain live virus particles that have been modified (or attenuated) to replicate in the animal but NOT cause disease in the animal.  The replication of the virus in the animal given an MLV vaccine is what stimulates the immune system.  The killed vaccines are safer, but tend to stimulate immunity only for a year or two.  Also, killed vaccines should be given at least twice during the initial vaccination procedure to be effective.  The MLV vaccines stimulate the immune system to produce the type of immunity that lasts longer, but may not be safe for pregnant animals.

The BVD vaccine you use should have both type I and type II BVD included.  Both of these biotypes (type I and II) are important in terms of causing disease, thus both should be included in the vaccine(s) you use.  Both type I and type II viruses should be included in both killed and MLV vaccines.  Also, since MLV vaccines produce longer lasting immunity it is important to use a good quality MLV vaccine at least once in calves.  This may be prior to weaning, at weaning, or 1-2 weeks after weaning; whenever, stress is least.  Afterwards, boosters of either MLV or killed vaccines can be effective as booster vaccinations.  Alternatively, a killed vaccine can be given to calves at branding followed by an MLV vaccine near weaning.

How do I keep BVD out of my herd?

BVD is a very common virus, so it may not be practical to try to prevent all possible methods of introduction.  However, “good fences make good neighbors” and this is true for prevention of many diseases such as BVD and Trichomoniasis.  Visitors who come into direct contact with your cattle should always have clean boots and clothes.  If not, supply them with these or restrict contact.  Quarantine incoming cattle and restrict your purchases of cattle to reputable sources that have information on their prevention programs.

What about Persistently Infected (PI) cattle?

Remember, these BVD persistently infected (PI) cattle are the ones that can shed enormous amounts of virus into your herd.  If you have “poor doing” cattle that you suspect may be PI, have them tested!  Your veterinarian can take ear notch samples or blood samples and the laboratory can identify these PI cattle.  You can then get rid of them.

What are the bottom line things I need to accomplish to prevent BVD problems?

1. Develop a good management system to prevent disease in general.
2. Work with your veterinarian to design a strong BVD vaccination program including the right type of vaccines and the right timing of administration.
3. Use the vaccines according to Quality Assurance standards.  Be particularly careful with MLV vaccines as they can be destroyed by heat, cold, sunlight, and contact with disinfectants.
4. Catch BVD problems early!  Diagnose abortions, weak calves, diarrhea cases, ill thrift cattle, and persistently sick cattle with the help of your veterinarian and laboratory backup.  Be sure you know what you are fighting.
5. Have a workable biosecurity plan.  

John Maas, DVM, MS
Diplomate, ACVN & ACVIM
Extension Veterinarian
School of Veterinary Medicine
University of California, Davis