Association of fertility traits with embryo development and pregnancy establishment

Selection for fertility traits, such as daughter pregnancy rate (DPR), heifer conception rate (HCR), and cow conception rate, has been shown to improve pregnancy success within dairy herds. This study explored the relationship between fertility traits and embryo development in both in vitro and in vivo conditions in dairy cattle. Data from 2,408 in vitro-produced (IVP) and 1,801 in vivo-derived (IVD) embryo procedures were analyzed. Embryos produced in these procedures were classified by quality (grade 1, 2, and 3). We assessed the relationship between fertility traits (DPR and HCR) and various embryo development parameters, including the total number of structures collected, blastocyst rate, and embryo quality, using generalized linear models. The analysis focused on female Holstein donors aged 10 to 20 mo. Fertility traits did not show a significant association with in vitro embryo production. However, in vivo, higher fertility values for DPR and HCR were associated with improved blastocyst rates, suggesting that these fertility traits may have a greater influence on embryo development in vivo. In addition, higher HCR values in the embryo were associated with increased pregnancy per transfer by d 30 when embryos were transferred into both heifers and cows, resulting in more calves born. Higher DPR values were also associated with a higher proportion of calves born when embryos were transferred to cows, indicating the potential influence of DPR on pregnancy outcomes in lactating cows. Our findings show that fertility traits DPR and HCR are associated with improved embryo development and competence to establish pregnancy, highlighting the potential for selection for embryo developmental and reproductive success. Further research is needed to better understand the mechanisms underlying these effects and to identify genetic markers and individual genes that could enhance fertility outcomes.