The increasing popularity of embryo transfer has implications for U.S. dairy cattle fertility evaluations

A.M. Miles*, J.L. Hutchison, and P.M. VanRaden

Animal Genomics and Improvement Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705-2350

2022 J. Dairy Sci.


Embryo transfer (ET) use has grown exponentially, with 11% of U.S. dairy calves born in 2021 attributable to ET. However, the trend in ET breeding event reporting does not parallel the ET calving rate and this lack of congruence can interfere both with national evaluations and on-farm management of fertility. Completely censoring ET-associated records is not necessarily the desired approach, as these represent the most elite animals and herds, and unreported ET could also bias fertility trait evaluations in the population. We propose an edit to account for incorrect ET reporting and explore its impact on sire conception rate (SCR), as an example. Data were extracted from the National Cooperator Database maintained by the Council on Dairy Cattle Breeding in December 2021, representing the most current information available on ET use in the USA. Reported mating types were matched with recorded birth types to assess ET reporting error rates. Only 1% of ET calves correspond to ET breeding events, 2% are incorrectly reported as artificial insemination, and 97% have no associated breeding event. Herdyears that reported >10% of calves born by ET but less than half of the expected ET breeding events given the number of ET calves born were removed, maximizing data preservation while minimizing confounding bias. SCR was recalculated for this new dataset and subsequent analysis showed that censoring herdyears with inconsistent ET reporting has a negligible effect on SCR overall, except in the case of elite young bulls popular for ET use. Similar edits for unreported ET had larger effects on heifer conception rate than cow conception rate or SCR and might be needed for other fertility-related traits. The rapid increase of ET is likely to continue as advanced reproductive technologies become more affordable. Censoring herdyears with inconsistent ET reporting has overall negligible effect, except for elite new bulls that have a huge influence on breeding programs. There is an urgent need to improve ET reporting to facilitate the delivery of accurate fertility evaluations.

Keywords: embryo transfer, conception rate, fertility, national evaluations