Breed and Season: Key Determinants of Efficiency in Large-Scale Commercial In Vitro Sheep Embryo Production

The efficiency of the laparoscopic ovum pick-up and in vitro embryo production (LOPU-IVEP) system in sheep is influenced by a complex interplay of genetic and environmental factors. This study comprehensively evaluated the effects of breed, season, and their interaction on oocyte retrieval, embryonic development, and pregnancy outcomes. A 20-month longitudinal analysis was conducted on a large commercial cohort comprising five breeds: Black-headed Suffolk (n = 3,024), White-headed Suffolk (n = 699), Australian White (n = 760), Black-headed Dorper (n = 1,109), and East Friesian (n = 1,077). We found that breed was the predominant factor affecting oocyte quantity and initial quality, with East Friesian yielding the highest number of total and available COCs. In contrast, season exerted a stronger influence on developmental competence, with autumn and winter providing optimal conditions, resulting in the highest cleavage rates (64.05%), blastocyst rates (59.02%), and pregnancy rates for single embryo transfer (73.04-75.31%). A significant breed-by-season interaction further identified Black-headed Suffolk in autumn/winter as a superior combination for embryo production. Correlation analysis revealed that oocyte quantity parameters were not predictive of developmental potential or pregnancy success. Our findings advocate for a precision management strategy that aligns the LOPU schedule with breed-specific seasonal advantages to maximize annual embryo production efficiency.