The virus is primarily transmitted through inhalation or ingestion of the virus from saliva, urine, faeces or discharges of an infected individual. The virus then may enter the blood stream of the susceptible animal and eventually settle in the reproductive tract. Infected bulls can shed virus in semen and semen quality may be altered. A susceptible cow bred by an infected bull that is shedding virus or bred artificially with infected semen may become a repeat breeder. Repeat breeding seems to be the result of failure of conception.
Fertility usually returns to normal after immunity develops.
As with bovine herpesvirus 1, there is no treatment for BVD virus related reproductive failure. Control is accomplished through a good vaccination program. Several killed and modified live virus vaccines are commercially available. The choice of a vaccine should be made by the producer in consultation with a veterinary practitioner. There are other bacteria and viruses that are known to interfere with reproduction, but the five discussed here are the most common and important threats to cattle production in Western Canada.