Using prostaglandin F2α and gonadotropin-releasing hormone simultaneously 7 d prior to Ovsynch increased first-service pregnancies per artificial insemination compared to Presynch-14/Ovsynch

Fertility programs such as G6G and Double-Ovsynch improve reproductive performance in lactating dairy cows following first service compared to cows inseminated following estrus. However, implementation of these programs in dairy operations can be logistically challenging due to hormone treatments on 4 different days of the week, which increase labor requirements and risk of program compliance issues. To simplify reproductive management, some dairy producers prefer to use Presynch-14 that concentrates most treatments on the same day of the week as day of pregnancy diagnosis. When combined with estrus detection, this strategy allows the insemination of a high percentage of cows ( ~ 50%) following the end of voluntary waiting period, which usually coincides with the second PGF2α treatment. However, this program might limit fertility performance since a high percentage of cows receiving timed-AI do not ovulate to the 1st GnRH of Ovsynch and may not be synchronized at time of insemination. Recently, a simpler pre-synchronization program for first service (PG+G), that uses PGF2α and GnRH simultaneously 7 d prior to Ovsynch, had similar ovulation rates to the 1st GnRH of Ovsynch and pregnancy per AI (P / AI) compared with fertility programs. This PG+G program could benefit dairy operations that use Presynch-14 since they would not need to change the weekday of injections, and reproductive performance could potentially increase. The aim of this study was to compare some physiological parameters and first-service P / AI of PG+G vs Presynch-14 in lactating dairy cows.