Bovine herpes virus-1: Comparison of methods for removal of a commercially important pathogen from cattle sperm, oocytes and pre-implantation embryos

Bovine herpesvirus 1 (BoHV-1) is a pathogen of major veterinary importance, causing principally reproductive failure, genital and respiratory disease in cattle. Since embryo transfer is a rapidly growing commercial venture, BoHV-1 has a significant negative impact on cattle breeding by both natural and artificial service, and thereby on the global livestock industry. Clinical infection of the reproductive tract causes infertility, early embryonic death and abortion. BoHV-1 may infect an embryo by either of two means. The first is through entry of contaminated sperm into the oocyte at the point of fertilization, while the second is via contact with either contaminated follicular fluid, oviductal or uterine tissues. In addition, the virus may infect the recipient cow if an infected embryo is transferred by assisted reproduction technology. This article briefly examines the two principal methods that are routinely available to eliminate BoHV-1, performed in order to prevent infection of bovine embryos. Although each offers considerable benefits, it is also imperfect. Even after multiple trypsin washes BoHV-1 can adhere to the zona pellucida of oocytes and pre-implantation stage embryos; likewise, cryopreservation fails to eliminate all infectious virus particles. A more experimental technique, sperm processing, shows considerable promise but requires further validation as an effective way to remove BoHV-1 from bull semen before it can be recommended for industry-wide use.