Reproductive and Perinatal Outcomes of Embryo Transfer in Elite Hanwoo Cows

Veterinarians should be vigilant in limiting embryonic, foetal and neonatal losses through appropriate reproductive programs and management strategies following natural mating and artificial insemination, especially after embryo transfer (ET) procedures, due to their high associated costs in Elite Hanwoo breeding programs. To establish a breeding population of Hanwoo cows with top 1% genomic estimated breeding values (GEBVs) for carcass weight and compare reproductive outcomes between OPU-IVF and MOET. Elite donor cows were assigned to either OPU-IVF or MOET groups, and the resulting embryos were transferred to synchronized recipient cows. Pregnancy rate, calving success, abortion, birth weight, sex ratio and dystocia were evaluated. The MOET group showed 100% calving success with no abortions; the OPU group had a 68.2% calving rate and 31.8% abortion rate. The sex ratio of the resulting offspring was similar between the groups, with female calves accounting for 37.5%-40.0% and male calves for 60.0%-62.5% of total calves. While the mean birth weights of female calves did not significantly differ between the groups (32.0-32.8 kg), male calves from the OPU group exhibited a significantly higher average birth weight (36.9 kg) than those from the MOET group, with a mean difference of 4.9 kg (p < 0.05). Spontaneous calving was more frequent in MOET (62.5%), while induced parturition was common in OPU (56.7%). Dystocia incidence was higher in OPU, especially with early induction. OPU-IVF was linked to higher abortion and dystocia risks, while MOET showed more favourable calving outcomes. Appropriate embryo production strategy and careful periparturient management are crucial for successful Hanwoo reproduction.