186 TRANSMISSION OF NONCYTOPATHIC BOVINE DIARRHEA VIRUS BY INFECTED SEMEN TO EMBRYO DONORS AND BY EMBRYOS TO EMBRYO TRANSFER RECIPIENTS AND OFFSPRING

Bovine diarrhea virus (BVDV) causes a variety of economically important enteric and infertility problems. For that reason, several countries have eradicated the disease and some others have schemes in progress to achieve freedom from it. Although there is a considerable amount of information about the risk of BVDV transmission through contaminated semen used for AI, there is no available evidence to indicate whether the resulting embryos, when used for embryo transfer (ET), can lead to the transmission of BVDV to recipients and offspring. For this experiment, semen from a bull persistently infected with BVDV (105 TCID50/mL of NY strain) was used for insemination (2 times at estrus) of BVDV-seronegative, superovulated heifers (n = 27).All heifers seroconverted to BVDV within 10 days post-insemination. Embryos and unfertilized oocytes were collected nonsurgically (n = 92) or postmortem (n = 52) 7 days post-insemination and were either washed according to IETS recommendations (without trypsin treatment) or left unwashed. In total, out of 144 unfertilized oocytes and embryos collected, 23 (16%) were of ET quality. Most of the embryos were degenerated or unfertilized. On 17 occasions, 1 or 2 washed embryos were transferred to BVDV-seronegative recipients. After ET, all pregnant and nonpregnant recipients remained free of BVDV and antibodies. In total, 6 heifers became pregnant and 5 calves free of BVDV and BVDV antibodies, including 2 sets of twins, have been born to date. Post-insemination, BVDV was detected in 29% (12/41) of unwashed and 10% (4/40) of washed embryos, 100% (4/4) of follicular fluid samples, oviductal epithelial cells, endometrium, and corpora lutea tissues as determined by the virus isolation test. Results herein suggest that BVDV can be transmitted by AI, resulting in the production of some proportion of contaminated embryos. However, it appears that such embryos, when washed according to the IETS guidelines, do not cause BVDV transmission to recipients or their offspring.