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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 superovulated dairy cattle 7 d after estrus. From 217 superovulated dairy cows and heifers, 2,211 eggs were recovered, of which 1,495 were classified as transferable embryos based on morphological evaluation of developmental stage and quality. From the evaluated embryos, 1,429 were non-surgically transferred to recipients to produce 623 calves. The transferable embryos were classified into five developmental stages and four 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 associated with the developmental stage and quality grade of the embryos: donor breed, parity, gonadotropin preparation, embryo sex, insemination bull, 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 was concluded that the developmental stage of embryos recovered at d 7 from superovulated cattle, when evaluated by simple morphological criteria, 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 embryo's quality grading was influenced by the embryologist. Consequently, sexing of an embryo recovered from superovulated cattle is not possible by simple morphological evaluation of the embryo's developmental stage.