Comparison of Two CIDR Synchronization and AI Treatments in Postpartum Lactating Bos indicus X Bos taurus Cows1,2

On d 0 of the experiment Bos indicus x Bos taurus (n=130) cows received an injection of GnRH and a progesterone-releasing device called an Eazi-BreedTM CIDR® for 7 d with a prostaglandin F2a injection at CIDR removal. Upon CIDR removal cows were divided into two AI treatments: 1) injection of estradiol cypionate (ECP) 24 h after CIDR removal with AI 8 to 10 h after a detected estrus and timed-AI 48 h after ECP for cows not exhibiting estrus (ECP treatment; n=67); or 2) estrous detection for 72 h with AI 8 to 10 h after a detected estrus and timedAI plus GnRH at 80 h for cows not exhibiting estrus by 72 h after CIDR removal (Non-ECP treatment; n=63). More (P<0.05) ECP cows (94.0%) exhibited estrus than Non-ECP (47.6%) cows during the 3-d estrous detection period and conception rates were similar between Non-ECP (68.8%) and ECP (57.1%) cows that exhibited estrus. Overall AI pregnancy rates were similar between the ECP (58.2%) and Non-ECP (50.8%) treated cows. Although, more ECP cows exhibited estrus, overall pregnancy rates were similar between the two AI treatments after the 7-d CIDR treatment. Postpartum lactating Bos indicus x Bos taurus cows synchronized with a 7 d CIDR had similar overall AI pregnancy rates between two AI treatments including an estrogen induced estrus combined with a timed-AI for cows not displaying estrus during the synchronized period (58.2%) and a 3-d estrus detection combined with a timed-AI plus GnRH for cows not displaying estrus during the synchronized period (50.8%). INTRODUCTION Previous research in our lab reported that administering GnRH at insertion of a 7-d progesterone-releasing device known as the Eazi-BreedTM CIDR® followed 7 d later with a prostaglandin PGF2a (PGF2a) injection provides the basis for an effective synchronization system in Bos indicus x Bos taurus cows. Upon CIDR removal cows can either be inseminated after a detected estrus, timed-AI, or a combination of the two. Previous research presented in this beef report (page 87) indicated that two CIDR synchronization and AI programs resulted in acceptable pregnancy rates in Bos indicus x Bos taurus cows. The two AI protocols included an injection of estradiol cypionate (ECP) 24 h after CIDR removal with AI 8 to 10 h after a detected estrus and timed-AI 48 h after ECP for cows not exhibiting estrus or estrous detection for 72 h with AI 8 to 10 h after a detected estrus and timedAI plus GnRH at 80 h for cows not exhibiting estrus by 72 h after CIDR removal. Both AI protocols provided acceptable pregnancy rates although experimental numbers were limited.