Effects of Early Postpartum GnRH and Prostaglandin F2α Administration on Reproductive Activity and Ovulation Synchronization in Lactating Dairy Cows

摘要

The objectives of this study were to determine the efficacy of GnRH and PGF2α for inducing early Postpartum (PP) estrual activity, hastening uterine involution and enhancing ovulation synchronization in lactating dairy cows. About 40 Holstein and Jersey cows were assigned at calving to 1 of 3 Treatments (Trt) and balanced by breed: Trt 1 (Control; n = 13) received an injection of saline on days 15 and 25 PP; Trt 2 (n = 14) received saline and PGF2α injections on days 15 and 25 PP, respectively; Trt 3 (n = 13) received GnRH and PGF2α injections on days 15 and 25 PP, respectively. Reproductive function was monitored through day 58 PP via electronic heat detection, rectal palpation for uterine tone, ultrasonography of ovarian structures and blood samples obtained 3 times week-1 for serum Progesterone (P4) analysis. On day 58 PP, an ovulation synchronization protocol was initiated as follows: GnRH given on day 0, PGF2α administered on day 7, GnRH given again on day 9 and artificial insemination conducted 16 h after the 2nd GnRH injection. In both Trt 2 and Trt 3, serum P4 fell sharply after the PGF2α injection at 25 days PP. An interaction of treatment by sample time (p<0.05) associated with treatment effects (PGF2α vs. saline) on P4 concentrations was observed. Postpartum estrual activity (p>0.10), rate of uterine involution (p>0.05), follicular dynamics (p>0.10) and P4 concentrations (p<0.10) did not differ between treatment groups prior to ovulation synchronization. Pregnancy rate following artificial insemination also did not differ between breeds (p>0.05) or among treatment groups (p>0.05) and for all cows was 50% (20/40). In summary, early postpartum hormonal treatments did not influence uterine involution, follicular development or estrus activity compared to non-Treated controls (Trt 1). Moreover, early postpartum (days 15-25 PP) treatment with GnRH and/or PGF2α did not enhance subsequent ovulation synchronization nor conception rates for lactating dairy cows in this study.