Effects of gonadotropin releasing hormone and prostaglandin F₂α on the reproductive performance in postpartum cows

A study was conducted to determine whether treatment with gonadotropin releasing hormone (GnRH) in combination with prostaglandin F₂α (PGF₂α) could enhance ovarian activity and uterine involution in postpartum dairy cows to reduce the calving interval. Cows were randomly assigned to one of three treatment groups. Cows (n = 8) in Group 1 received 100 μg GnRH intramuscularly (i.m.) twice on Day 20 and Day 35 postpartum, and 25 mg PGF₂α i.m. on Day 47 postpartum. Group 2 (n = 8) received a single i.m. injection of 100 μg GnRH on Day 25 postpartum and 25 mg PGF₂α i.m. on Day 37 postpartum. The Control Group (n = 9) did not receive hormonal treatment. Palpation per rectum of the reproductive organs and serum progesterone (P) determination were performed twice a week to monitor ovarian activity and uterine involution. Postpartum interval to the first ovulation was short in treated groups (Group 1, 21.0 d; Group 2, 26.3 d) compared with Control Group (30.1 d, P < 0.05). Likewise, mean frequency of ovulation was increased in both treated groups compared with the Control Group (P < 0.05). Cows in treated groups required fewer days to complete uterine involution than in the Control Group. The mean interval to the first service, the conception rate at first service and the number of services per conception showed no significant differences among the three groups, but the mean days from calving to conception were shorter for the treated groups (78.7 d in Group 1; 83.3 d in Group 2) than (109.1 d, P < 0.05) for the Control Group. Our results suggest that combined treatment with GnRH and PGF₂α may enhance ovarian activity in the postpartum cow, resulting in improved reproductive performance.