– William P. Shulaw DVM MS, Extension Veterinarian, Beef/Sheep, The Ohio State University
Vaccines are one of the tools producers use to protect the health of their breeding herd. Like providing adequate energy and protein at critical times, a trace mineral supplement, and clean calving areas, vaccines do not provide absolute protection but are a part of the total heath program. The most common ones used by producers are for the viruses – infectious bovine rhinotracheitis (IBR), bovine virus diarrhea (BVD), parainfluenza (PI3), and bovine respiratory syncytial virus (BRSV) – and five types of the bacteria we call Leptospira or ‘lepto’ as it is commonly called. All four viruses are involved in the respiratory disease complex we used to call shipping fever, but IBR, BVD and Leptospira also cause abortions, embryonic deaths and failure of the cow to conceive.
Of the virus vaccines, we have a choice between modified-live virus (MLV) and killed virus preparations. Each type has its own advantages and disadvantages and some of these have been outlined in previous articles in this newsletter. For the beef breeder, perhaps some considerations of each are occasionally overlooked. Killed virus vaccines are generally considered very safe, have no potential to cause shedding of virus, and can be given to pregnant animals. However, they may be less efficient in stimulating the full range of the immune response than the MLV vaccines.
The MLV vaccines are usually cheaper and may better stimulate the cellular response side of the immune system than killed virus preparations because they act more like a real infection. However, the virus in some MLV vaccines, such as some of the intra nasal vaccines for IBR, can occasionally be shed for a few days from the nasal passages. This particular IBR virus has been modified so it is safe for pregnant animals, but shed vaccine virus may stimulate an antibody response in a non-immune, or susceptible animal. Usually this is a good thing. But if you are selling or leasing bulls to an artificial insemination center, vaccination of the bull or its recent exposure to vaccinated animals may cause it to be positive for IBR virus when tested. This may cause the bull to be rejected, or it may require the bull stud to house and manage the bull apart from the IBR-negative animals. This is particularly true for dairy bulls. For example, the commercial AI centers (according to Dr. Don Monke of Select Sires) are requiring that dairy bull calves be antibody negative and not vaccinated for IBR. Although beef bulls that have been vaccinated for IBR continue to be accepted by both commercial and custom AI Centers, the international marketability of semen from selected beef bulls could be enhanced if they were not exposed to IBR virus, and IBR vaccine virus, prior to entrance to an AI Center.
Most producers know that the MLV vaccines for IBR, PI3, and BVD are not labeled for use in pregnant cows or in calves nursing pregnant cows. Although it is not known how often it could be a real problem in the field, some experimental work suggests that the injectable MLV IBR and BVD viruses can cause inflammation of the ovary. Therefore, producers are often cautioned not to knowingly use them within 30 days of the onset of breeding season in order to avoid the possibility of reduced conception. So, how do we use these tools? There are lots of opinions and approaches to using these vaccines. As in many other things in life, this usually means no one approach is always best. A compromise approach advocated by some is to use the MLV vaccines in replacement animals after weaning. Two doses given after six months of age, and at least 30 days before breeding, are often recommended. This provides an opportunity to stimulate the immune system with a vaccine that behaves similarly to a real infection, but at a time when there is no risk to conception or the fetus. Killed virus vaccines can then be used to booster the immune response in adult animals. This is usually done annually. Alternately, boosters with MLV vaccine can be given in the open period, but timing this can be difficult for some producers. Because often the most serious complication of infection with one of these viruses in cows is abortion, producers and their veterinarians may choose to give booster vaccinations for IBR, BVD and lepto relatively near the time when the risk is greatest – before mid-gestation.
Producers should sit down with their veterinarian, explain their goals and usual management of the breeding herd, and then develop a vaccination plan that best fits their herd’s needs.