Strategies to improve fertility of Bos taurus beef females enrolled in estrous synchronization protocols
Estrous synchronization (ES) protocols enhances profitability of beef cow-calf operations by improving percentage of cows pregnant early in the breeding season and increasing kg of calf weaned per cow exposed. Many factors, however, influence the fertility of cattle enrolled to ES protocols. The overall goal of this work was to determine the influences of estrus expression and timing of artificial insemination (AI), as well as temperament on fertility of Bos taurus beef females exposed to ES protocols. Multiparous cows (n = 1,676) were enrolled to the 7-d CO-Synch+ Controlled internal drug releasing device (CIDR) protocol and cows expressing estrus were inseminated. Cows not expressing estrus received a gonadotropin-releasing hormone injection and were either inseminated immediately or delayed by 8 hours. Pregnancy rates were greater for cows expressing estrus to the protocol. Delaying AI for 8 hours in cows that failed to express estrus did not improve pregnancy rates. The effects of temperament on fertility of beef heifers enrolled to the 7-d CO-Synch+CIDR protocol were investigated. Heifers (n = 297) had temperament assessed by chute score and exit velocity, and classified as adequate or excitable. Hair and blood were collected for cortisol evaluation. Pregnancy rates were greater for adequate temperament heifers. Circulating cortisol concentrations were greater for excitable heifers, and overall plasma and hair cortisol concentrations were reduced from the start of the protocol to the end. Heifers with adequate temperament have improved fertility and ES protocols acclimated heifers and reduced plasma and hair cortisol concentrations due to handling.