FACTORS AFFECTING THE DEVELOPMENTAL STAGE OF EMBRYOS RECOVERED ON DAY-7 FROM SUPEROVULATED DAIRY-CATTLE

The objective of this retrospective study was to evaluate the factors influencing developmental stage of bovine embryos recovered from super ovulated dairy cattle 7 d after estrus. From 217 superovulated dairy c ows and heifers, 2,211 eggs were recovered, of which 1,495 were classi fied as transferable embryos based on morphological evaluation of deve lopmental stage and quality. From the evaluated embryos, 1,429 were no n-surgically transferred to recipients td produce 623 calves. The tran sferable embryos were classified into five developmental stages and fo ur quality grades. The least-developed transferable embryos tended to be classified into poorer quality grades. A multifactorial statistical model was used to analyze whether the following factors were associat ed with the developmental stage and quality grade of the embryos: dono r breed, parity, gonadotropin preparation, embryo sex, insemination bu ll, embryologist (the person evaluating the embryo), year, and season of recovery. Among these factors, only the embryologist and the donor animal accounted for significant variation in embryo development. It w as concluded that the developmental stage of embryos recovered at d 7 from superovulated cattle, when evaluated by simple morphological crit eria, was correlated with the embryo's quality and was affected by the donor animal but in this study not by the embryo sex, donor breed and parity, gonadotropin preparation, and insemination bull used. The emb ryo's quality grading was influenced by the embryologist. Consequently , sexing of an embryo recovered from superovulated cattle is not possi ble by simple morphological evaluation of the embryo's developmental s tage.