Long-term CIDR program for synchronization of estrus in beef heifers produces acceptable AI pregnancy rates



Journal Title

Journal ISSN

Volume Title


Kansas State University. Agricultural Experiment Station and Cooperative Extension Service


Routinely achieving pregnancy rates greater than 50% with fixed-time artificial insemination (AI) in heifers has been difficult. The Beef Reproduction Task Force recently added the intravaginal progesterone-releasing device (CIDR)-Select to its list of recommended fixed-time AI protocols. Research and field trials in Missouri have achieved AI pregnancy rates in the range of 55% to 60%. Another relatively new protocol is the 5-day CO-Synch, a timed AI protocol + CIDR that has produced pregnancy rates similar to or higher than those obtained with the standard 7-day CO-Synch + CIDR protocol. It is not known whether these two systems differ in terms of estrous response. The objective of the current study was to compare effects of a long-term, 14-day CIDR-Select protocol and a 5-day CO-Synch + CIDR protocol on estrous distribution and AI pregnancy rate in yearling beef heifers.



Beef, CIDR, Estrus, Heifers, AI, Pregnancy rates