Effects of embryo production method and day of transfer post-estrus into recipients on pregnancy rates with bovine embryos

Abstract

Bovine embryo transfer is a way to capitalize on superior genetics of donor cows in the beef and dairy industries. The two common types of embryo production: in vitro fertilization (IVF) and conventional (in vivo), consist of different processes that could affect pregnancy rates. Also, day of embryo transfer post-estrus in the recipient often varies in practice. The objective of this study was to evaluate potential effects of embryo production method and day of transfer post-estrus in recipients on pregnancy rates to embryo transfer. Cows entered the chute at random and embryos were placed into the recipient using standard insertion procedures by a certified veterinarian. Cows were pastured and fed daily on a customized total mixed ration during the process. Recipient cows were ultra-sounded 60 d post insertion date by a veterinarian to determine pregnancy status. Data were collected and categorized in a 2x2 factorial design. Factor 1 was embryo production method: IVF or conventional fertilization. Factor 2 was the day embryos were transferred into recipient cows post-estrus: early (d 4, 5, or 6) or typical (d 7 or 8). Data were analyzed using the GLIMMIX procedure of SAS with an alpha value of 0.05. There was no significant interaction between embryo production method and day placed post-estrus on pregnancy rates (P = 0.228). There was no significant effect of embryo production method on pregnancy rates (P = 0.764). There was also no effect of day placed post-estrus on pregnancy rates (P = 0.631). Producers synchronizing multiple recipient females with variation in day post-estrus and (or) using embryos produces by either IVF or conventional methods can expect similar pregnancy rates to embryo transfer. Overall, analysis with additional data and reproduction factors such as age and number of parities of recipients would be beneficial to determine effects on pregnancy rates with bovine embryos.