Comparison of the Effects of Gonadotropin-Releasing Hormone, Human Chorionic Gonadotropin and Progesterone on Conception Rates in Repeat Breeder Dairy Cows

Abstract

A slower than normal rise in progesterone concentrations and a lower total progesterone concentrations have been measured in low-fertility cows and repeat breeder (RB) heifers in the first six days after estrus. Several methods have been used to attempt to increase conception rates (CR) through a greater plasma progesterone (P4) concentrations during the luteal phase, including those that increase endogenous function of the existing corpus luteum (CL), induce accessory CL, or act as a direct progesterone supplement. The aim of the present study was to determine whether supplementing with exogenous P4 or the administration of gonadotrophin-releasing hormone (GnRH) or human chorionic gonadotrophin (hCG) during early luteal phase could increase CR in RB cows.