First-service pregnancy rate in beef heifers as influenced by human chorionic gonadotropin administration before and/or after breeding

Two experiments were conducted to evaluate whether administration of human chorionic gonadotropin (hCG) before and/or after breeding influences the first-service pregnancy rate in beef heifers. In Experiment 1, 125 yearling and two-year-old heifers were allotted to one of four groups: a control group; a group receiving 3,000 IU hCG on Day 4 of the prebreeding estrous cycle; a group receiving 3,000 IU hCG on Day 4 post breeding; and a group receiving 3,000 IU hCG on Day 4 of the prebreeding estrous cycle and again on Day 4 post breeding (Day 1 = estrus). First-service pregnancy rate was not affected by a single intramuscular (i.m.) injection of 3,000 IU of hCG on Day 4 of the prebreeding estrous cycle and/or post breeding. In Experiment 2, 111 yearling heifers were allotted either to an untreated control group or to a group receiving 3,000 IU hCG on Day 4 post breeding. Administration of a single i.m. injection of hCG on Day 4 post breeding did not affect the first-service pregnancy rate.