Efficacy of Sequential Estrus Synchronization and Timed Artificial Insemination in Beef Cattle Beginning 19 days after an Initial Timed Artificial Insemination

A breeding program utilizing single fixed-timed artificial insemination (AI) was compared to a resynchronization program for a second fixed-timed AI. Angus and Angus cross primiparous and multiparous cows were randomly assigned to one of two treatment regimens; either single TAI (CON; n=468) or two sequential TAI (RS; n=473). The main objectives were assessing pregnancy rates and analyzing fetal age to estimate calving distribution rates between the two treatment groups. The 7-day CO-synch + CIDR protocol was utilized in both treatment groups to synchronize estrus for TAI-1 at 60h - 66h post- Prostaglandin injection (PGf2α). Animals in the RS treatment groups received an additional 7-day CO-synch + CIDR protocol 19 d after TAI-1. On d 26, both CON and RS animals were pregnancy checked via transrectal ultrasonography. At this time, RS animals diagnosed as not pregnant received an injection of PGf2α, and an Estrotect® estrous detection aid was applied. All nonpregnant RS cows received a second TAI (TAI-2) and GnRH injection 60-66h after PGf2α (day 29). Additional pregnancy checks were initiated on the following days relative to TAI-1, d 60, and d 120.There was no difference in pregnancy rates post TAI-1 (P