Clinical use of human chorionic gonadotropin in dairy cows: An update

Human chorionic gonadotropin (hCG) has a potent luteinizing hormone (LH)-like effect in cattle that extends the life span of the corpus luteum (CL) and increases progesterone synthesis, induces ovulation throughout the estrous cycle, promotes the formation of accessory corpora lutea when applied in the early luteal phase, and modifies follicular wave dynamics increasing the frequency of three-wave dominant follicular cycles. As hCG acts on ovarian cells independently of the pituitary gland and its effect is longer lasting than that produced by endogenous LH release, use of hCG rather than gonadotropin-releasing hormone (GnRH) could be targeted at populations of subfertile cows. This review describes the clinical use of hCG to improve the reproductive performance of dairy cows. In addition, we describe recent developments in the therapeutic use of hCG and studies addressing the benefits of including hCG in estrus and ovulation synchronization protocols. Our review ends with a critical discussion of how earlier findings related to ovarian responses to hCG treatment can be interpreted in the light of recent advances in the clinical applications of hCG.