Response of dairy heifers to Prostaglandin F2alpha after treatment with human chorionic gonadotropin

After the observation of estrus following administration of Prostaglandin F(2alpha) (PGF(2alpha)), 79 dairy heifers were randomly either injected with 2500 IU of human chorionic gonadotropin (hCG) 48 h postestrus or maintained as controls with no injection at that time. Five to 9 d later, after a blood sample for progesterone determination was taken, all heifers were injected with 25 mg of PGF(2alpha). Heifers observed in estrus within the next 5 d were inseminated about 12 h after initial observation and were palpated for pregnancy 45 to 60 d postinsemination. Heifers treated with hCG had higher progesterone concentrations, reduced and delayed estrual responses, and lower insemination fertility rates when compared with control heifers.