Beef Heifer and Cow Estrous Synchronization Programs

Abstract

Recent estrous synchronization research has aimed to develop reliable protocols that: 1) rely solely on fixed-timed artificial insemination (TAI); 2) require a maximum of three animal handlings; and 3) are successful in estrous-cycling and non-cycling females. In cows, insertion of an intravaginal progesterone insert during the seven-day interval between the initial gonadotropin- releasing hormone (GnRH) and prostaglandin injections of the CO-Synch protocol enhanced pregnancy rates by 9 to 10%. Recent research has shown that TAI protocols yield pregnancy rates similar to a protocol involving detection of estrus plus a fixed-time cleanup AI for females not detected in estrus. Initiation of estrous cycles in· non-cycling cows is likely the primary manner in which beef producers may improve fertility in response to estrus synchronization and TAI protocols. Treatment of non-cycling females with progesterone and GnRH increases the percentage of cycling females and improves fertility to a TAI, but inducing cyclicity with human chorionic gonadotropin (hCG) fails to enhance fertility in TAI protocols. Supplementing progesterone after TAI fails to increase pregnancy rates in beef cattle. In contrast, administration ofhCG seven days after TAI induced an accessory corpus luteum, increased progesterone, and tended to enhance pregnancy rates. Use of TAI protocols reduces the hassle factors associated with ovulation synchronization and AI, and provides cattle producers efficient and effective tools for capturing selective genetic traits of economic consequences. Location variables, however, such as differences in pasture and diet, breed composition, body condition, postpartum interval, climate, and geographic location, affect the success of TAI protocols.