10 New insights to sire influence on embryo health: evaluating embryo morphokinetic activity in top TPI Holstein bulls

Breeding bull selection is crucial for dairy and beef programs, and bulls possessing desirable genetic traits are in high demand and are used extensively in assisted breeding programs, including in vitro embryo production. Although expected progeny differences for production, health, and conformation are well studied, sire-influenced embryonic factors are rarely studied. Recently, real-time embryo morphokinetics has emerged as an objective means to measure cellular activity as it relates to embryo health, viability, and stress. As the embryo is critical to the reproductive success of these elite sires, objectives of this study were to evaluate embryo health and morphokinetics produced from top Total Performance Index (TPI) Holstein bulls and develop key metrics to evaluate sire-influenced embryo production for use in routine in vitro and in vivo embryo production. A total of 3198 Holstein embryos were produced from commercial IVF laboratories and shipped fresh to a Holstein breeding facility between May 2024 and July 2024. Upon arrival, embryos were evaluated by an embryologist. For the evaluations, a 30-s video of each embryo was recorded with a View 4k camera mounted to a Nikon SMZ 1270 microscope. Each embryo was transferred into an eligible recipient during routine embryo transfer, and pregnancy outcomes were obtained via ultrasound examination after transfer. The data set represents 107 total bulls. The numbers of embryos per bull were ranked, and the top five most frequent bulls were selected for this study, which produced 741 embryos that were deemed transferrable (at least a stage 6 and grade 1 or 2). Next, videos of these embryos were processed with EmVision R&D Software to quantify embryo morphokinetic activity. Mean morphokinetic activity and the standard deviation were calculated for each embryo, and results were grouped by sire. Results were analyzed with ANOVA and Pearson correlation coefficient using P < 0.05 for significance. As shown in Table 1, each bull produced 133–183 embryos, with pregnancy rates ranging from 39% to 51%. Analysis revealed a significant negative correlation (R = −0.906, P < 0.05) between pregnancy rate and mean embryo morphokinetic activity, indicating lower activity correlated with higher pregnancy success. Bull 5, with the lowest pregnancy outcomes, exhibited significantly higher morphokinetic activity (P < 0.001). This study emphasizes sire influence on embryo morphokinetic activity, which is critical for pregnancy success. Evaluating such activity can optimize embryo culture environments and improve pregnancy outcomes for elite bulls. These insights may also inform the calculation of TPI and shed light on heritable traits affecting reproductive efficiency. Current work is expanding this study to include more bulls from the existing data set.