Reproductive performance in experimentally BVDV infected ewes and seroconversion rates in sheep co-mingled with BVDV PI calves

Abstract

Bovine viral diarrhoea virus (BVDV) is an economically important disease of cattle, causing severe reproductive losses and immunosuppressive effects in cattle populations worldwide. Before a national BVDV control programme can be developed in Australia, it is important to explore the possibility of sources of transmission from and through alternative susceptible populations, such as sheep.Transmission of BVDV to species other than cattle has been shown to occur following both experimental and natural infection of other ruminants. The aims of this study were to investigate the impact of an experimental infection with a local Australian strain of BVDV (Type 1c) on the reproductive performance of pregnant ewes and the potential for natural transmission of BVDV from persistently infected (PI) cattle to naive sheep.Twenty-three BVDV naïve, pregnant ewes were experimentally infected with BVDV by subcutaneous inoculation with 2mL freeze-thawed PI cow serum. Severe reproductive losses including low lambing rates and a high number of young lamb deaths were seen in these ewes. One PI lamb was also produced in this trial, but died at 15 days of age.Nine BVDV naïve sheep wethers were co-mingled with three BVDV PI calves in a 1500sqm paddock for four weeks. Transmission of infection, as indicated by seroconversion, occurred in four of nine wethers during a four-week period of co-mingling.The trials suggest that the potential for infection with BVDV derived from cattle for sheep exists and needs to be taken into account when controlling BVDV infection in cattle.