The role of Bulls in BVD Transmission
George Caldow
Bulls play a major role in BVDV transmission. Since an infection with this kind of cattle disease can affect the quality of the semen, the performance of breeding bulls can suffer considerably. BVDV infection can reduce semen quality significantly and therefore poses a threat to the production targets of the herd. When it comes to PI bulls, the semen quality is almost always poor. Some bulls may still sire calves, but most of the time they are infertile.
If bulls are transiently infected with BVD virus, the semen production will be affected adversely for a couple of weeks. This reduction in quality will improve throughout a period of nine weeks through the spermatogenesis cycle. In total, this will result in a period of three months with a semen quality below normal standards which most likely renders the bulls infertile for that time.
If bulls are transiently infected with the BVD virus during puberty, they can produce virus contaminated semen for months, if not years. There are tests which can be used to screen the semen for the presence of BVD virus. However, it is desirable to prevent the transient infection rather than merely test the bulls’ semen. In order to achieve that, bulls should be reared in BVDV free herds that have tight bio-security at all times. Bulls should be sourced from those herds at least three months before they are introduced into a new herd. Prior to the introduction into a new herd, the bull should be isolated and should receive the same vaccinations as the cows do. Treating bulls this way can prevent the adverse effect on semen quality caused by BVD.
