Effect of embryo quality and developmental stages on pregnancy rate during fresh embryo transfer in beef heifers.

The objective of this study was to evaluate the effect of embryo quality and developmental stages on pregnancy rate in beef heifer recipients. The present study used 168 Simmental breed cows as donors, and 618 beef cattle breed heifers as recipients. The quality and developmental stages of the collected embryos were evaluated according to the criteria specified by the International Embryo Technology Society. Accordingly, the embryos in the compact morula, early blastocyst, blastocyst, and expanded blastocyst stages that were of Code I (excellent) and Code II (good) quality levels were transferred as fresh embryos to the recipient heifers. Prior to the transfer, the recipients were synchronized using the Ovsynch protocol, and the embryos obtained were transferred to 618 beef heifers. Pregnancy examinations were performed on days 30 and 60. On day 30, the pregnancy rates with Code I and Code II embryos were determined as 44.15% and 32.58%, respectively. According to the developmental stages, the pregnancy rates with Code I quality compact morula, early blastocyst, blastocyst, and expanded blastocyst were determined as 44.64%, 45.67%, 45.83%, and 33.33%, respectively. The rates of pregnancy with Code II quality compact morula, early blastocyst, and blastocyst were determined as 32.03%, 32.14%, and 50.0%, respectively. In conclusion, the pregnancy rates with Code I quality embryos were found to be higher compared with Code II embryos (P < 0.05). It was also determined that the embryonic developmental stages had no effect on the pregnancy rate (P > 0.05).