BVD is a serious cattle disease.

By Ian Wickham, September 2005.

Most dairy farmers in NZ are not aware of the effects of Bovine Viral Diarrhoea (BVD) in dairy herds, but it is estimated to cost them around $54 million per year.

Symptoms range from mild to severe diarrhoea. BVD suppresses the immune system, which can lead to other bacterial and viral infections. BVD infection is endemic in most NZ dairy herds and it is estimated that 1% to 2% of animals are PI.

While vaccination is an obvious tool to be used for control, it alone is not enough to eliminate the disease. A lot is now known about the special way the virus is carried by Persistently Infected (PI) animals, and it is the prevention of this ‘carrier animal’ being created that is crucial to the elimination of the disease. PI animals are created when their mother becomes infected during pregnancy. For a calf to be born PI, it must be infected between 90-120 days of gestation when immuno-competence is developing.

Potential Risk.

Because of the strict health tests applied to all Artificial Breeding semen production, it is extremely unlikely for the BVD virus to be carried in this way.

However, it is estimated between 72,000 and 96,000 bulls (non AB) are used as service bulls in the dairy industry each year, (mainly as ‘follow-up bulls’ after AB ends) but only about 2% of these are screened, of which 1% are persistently infected.

Unless all bulls are screened, in an average size herd this will translate into a 6-8% chance that a PI bull will be present and shedding virus.

"A surviving PI offspring will become a carrier for life with every cell in its body containing the virus."

NZGC Risk Management protocol for BVD.

New Zealand Grazing Co Ltd policy is to screen and cull all bulls for BVD PI ‘carriers’ and also vaccinate them to provide the maximum possible protection from spreading this virus through the heifers we care for during the critical mating season.

Very few of the calves born to first calving heifers are kept for dairy replacements in this country and it follows that the risk from introducing PI animals into the herd from this source must therefore be low.

Recommendation.

Discuss with your regular Veterinarian a suitable risk management protocol for your herd. If it includes a vaccination program for your heifers, notify us to include this in our regular program for your heifers.