Factors in cattle affecting embryo transfer pregnancies in recipient animals

The use of embryo transfer (ET) in cattle is important for profitability and improved genetic gains. The advent of the commercial embryo collection and transfer industry has led to advancements in multiple techniques and practices. Specific variables, however, have historically affected pregnancy rates but an understanding of the magnitude of these effects in the current industry is limited. Transfer location (cranial, middle, or caudal third of the uterine horn ipsilateral to the ovary with a CL), transfer score (range of 1-3 with 1 being excellent and 3 poor, based on difficulty of accessing the site of embryo deposition), and amount of time to complete a transfer, therefore, were recorded. These variables were collected in a setting designed to mimic commercial production practices as well as exaggerated time (due to data collection) to assess effects on pregnancy rates. Fresh and frozen in vivo-derived embryos (n = 256) from Bos taurus cows were transferred to Bos taurus recipients. There tended to be more pregnancies when embryos were deposited in the cranial part of the uterus (P =  0.08) compared to the middle and caudal third of the uterus. With a lesser degree of difficulty in transfers (score 1), there tended to be more pregnancies established (P =  0.07). When lesser time was needed for transferring embryos and collecting data, there were greater pregnancy rates (P =  0.03). Thus, these traditionally accepted variables of influence (site of embryo placement in uterus, difficulty, and time) continue to influence ET pregnancy success.