The Holstein cow in embryo transfer today as compared to 20 years ago.

ABSTRACT

Embryo transfer practice and results were examined over a 20-year period in Holstein cows and heifers within four commercial embryo transfer programs located in different areas of North America. Mean embryo production per collection decreased (P < 0.05) in one program over time, but not in the other three. Changes in the type of cows entering embryo transfer programs, the number of times they were superstimulated and changes in the brands of gonadotropins used for superstimulation all complicated the analysis of embryo production over time. Data reveal higher pregnancy rates (P < 0.001) following transfer of embryos into Holstein heifers than into lactating dairy cows. It is not clear whether pregnancy rates have decreased over time as a result of the change from surgical to non-surgical embryo transfer. In the two programs in which pregnancy rates were analyzed, there was a decrease (P < 0.001) when non-surgical transfers were adopted in one program, while no change occurred in the other. One of the biggest changes in all programs was that more than 50% of embryos recovered from donors are now frozen after collection, whereas the majority were transferred fresh 20 years ago.