12 Effect of additional prostaglandin F_2α during the Ovsynch protocol applied in different postpartum intervals in lactating dairy cows: Preliminary results

Abstract

Timed AI (TAI) programs have been developed to increase the service risk. However, when Ovsynch is used as a synchronization protocol, lack of regression of the corpus luteum after prostaglandin F_2α (PGF) administration has been demonstrated, leading to reductions in fertility. In this way, a second PGF administration might increase the frequency of achieving complete luteolysis. This study aimed to evaluate the effect of an additional treatment with PGF on fertility when an Ovsynch synchronization protocol was applied at different postpartum intervals. Multiparous high-production dairy cows (n = 471) of a commercial farm were stratified by postpartum intervals [<120 (n = 136), 120-150 (n = 131), 150-180 (n = 92), 180-210 (n = 52), and >210 days (n = 60)] and randomly allocated to receive either the Ovsynch (n = 108) or Ovsynch with second PGF protocol (n = 243). Cows inseminated 12 h after observed heat detection (AI) served as a control (n = 120). The Ovsynch protocol consisted of an injection of gonadotropin-releasing hormone (100 µg; Fertagyl®, Intervet, Millsboro, MD, USA) on Day 0, an injection of PGF (0.5 mg; Estrumate®, Schering-Plough Animal Health, Montréal, QC, Canada) on Day 7, another injection of gonadotropin-releasing hormone (100 µg) on Day 9, and timed insemination on Day 10. The Ovsynch with second PGF protocol consisted of the same hormone injection schedule as the Ovsynch protocol, but a second injection of PGF (0.5 mg; Estrumate®) was administered 24 h after the first PGF. Data were analysed using the chi-square test. The level of significance was taken as P < 0.05. When data were pooled at 120 to 150 days of postpartum interval, pregnancy rate was higher, but not significantly different (P > 0.05), for cows that received the Ovsynch (37.5%, n = 32) or Ovsynch with second PGF protocol (33.8%, n = 77) compared to nonsynchronized cows (22.8%, n = 22). After 180 days of postpartum interval, Ovsynch with second PGF protocol triggered pregnancy rates similar to those of nonsynchronized cows (33.3%, n = 21 and 28.6%, n = 14), whereas the Ovsynch protocol resulted in lower percentages (11.8%, n = 17; P > 0.05). Similar pregnancy rates (P > 0.05) were observed when TAI protocols were administered before 120 days (26.5 and 30.2% for Ovsynch and Ovsynch with second PGF, respectively) or between 150 and 180 postpartum days (31.8 and 33.9% for Ovsynch and Ovsynch with second PGF, respectively) compared with AI cows (25.7 and 28.8% for <120 days and between 150 and 180 postpartum days, respectively). These preliminary results showed a tendency of a better pregnancy rate when both TAI synchronization protocols were applied between 120 and 150 postpartum days when compared with AI. Also, the application of a second dose of PGF seems recommendable when the Ovsynch protocol is used to synchronize cows of >180 postpartum days. Ongoing research will allow an increase in the number of the samples in each postpartum interval in order to confirm these results.