Date of this Version
The recent development of methodology for the successful cryopreservation (Le., ultra low temperature freezing) of bovine embryos has expanded the opportunities for international movement of bovine embryos and has facilitated the exchange of germplasm within and among countries. Unfortunately, frozen embryos also provide an excellent vehicle for the distribution of pathogenic agents (e.g., bluetongue virus, foot and mouth disease, etc.) between livestock populations and between countries. Most pathogens that are on the surface of an embryo with an intact zona pellucida (a translucent mucopolysaccharide shell surrounding the embryo) can be removed by washing. The washing procedure consists of subjecting the embryos to 10 to 12 changes of medium, each change of medium resulting in a 100-fold dilution of the medium. However, some viruses (e.g., infectious bovine rhinotracheitis virus and vesicular stomatitis virus) adhere firmly to the zona pellucida and are not removed by the 10 to 12 changes of medium. The objective of this study was to determine the risk of transmitting the bluetongue virus by washed bovine embryos from infected cows. The present study was conducted with a sufficient number of animals to estimate the probability of bluetongue virus transmission by the transfer of embryos from an infected donor, to mimic as closely as possible the natural infection of embryo donors, and to collect the embryos at various periods during the donors' interaction with the virus.