Estrous response for progestin-based estrous synchronization protocols and subsequent pregnancy rates when using sorted semen in primiparous and multiparous beef cows

Abstract

Sorted semen is more costly and often results in lower pregnancy rates than unsorted semen. Therefore, it is important to identify estrous synchronization protocols that maximize expression of estrus and AI pregnancy rates when using sorted semen. Our laboratory has observed good synchrony and AI pregnancy rates for cows synchronized with a 14-day CIDR treatment, followed by GnRH on day 16 and prostaglandin F2 (PG) on day 23. In the absence ofluteal progesterone, a 14-day CIDR treatment should result in the development of a persistent follicle. Thus, our protocol might be improved by the addition of PG on day 7 of the CIDR treatment, to ensure endogenous progesterone concentration is low and that a persistent follicle will develop and respond to GnRH given on day 16. This study evaluated the estrous response and subsequent AI pregnancy rate after synchronization of beef cows with a 14-day CIDR protocol, with an additional PG treatment given on day 7 of the CIDR treatment. A secondary objective was to evaluate the effect of time of insemination after onset of estrus on pregnancy rate when sorted semen was used.