In Vitro Developmental Competence Predicts Pregnancy Outcomes Following Transfer of Beef Embryos to Dairy Recipients: A Retrospective Study

In bovine embryo transfer (ET) using in vitro-produced (IVP) embryos, recipient factors and embryo grade are well-established predictors of pregnancy success, but the impact of the laboratory-level developmental competence of IVP embryos remains insufficiently characterized. This retrospective study evaluated factors affecting pregnancy rates following the transfer of IVP beef embryos to dairy recipients. Medical records from 462 ETs were analyzed across three categories: (1) recipient-related factors (parity, body condition, estrus synchronization, corpus luteum characteristics); (2) laboratory factors (cleavage, blastocyst formation, degeneration, embryo grade, developmental stage, cryopreservation); and (3) environmental factors (temperature–humidity index, transport time). Mean comparison and chi-square analyses revealed significant differences in pregnancy rates based on corpus luteum volume, cleavage rates, blastocyst formation rates, degeneration rates, and embryo grade. In binary logistic regression, categorized increases in blastocyst formation rate, degeneration rate, and embryo grade were associated with a 1.45-fold increase, 0.74-fold decrease, and 0.56-fold decrease in pregnancy odds, respectively; no recipient or environmental variables were independent predictors. These findings indicate that developmental competence of IVP embryos is more critical for pregnancy success than recipient or environmental factors, suggesting that optimizing IVP systems to maximize embryo quality is the most effective strategy to improve reproductive efficiency in ET.