Oestrous response and characterization of the ovulatory wave following oestrous synchronization using PGF2α alone or combined with GnRH in ewes

- In sheep, inclusion of GnRH in an oestrus synchronization protocol shortened time to onset of oestrus.
- Treatment with GnRH resulted in more synchronized ovulation.
- Treatment with GnRH reduced number of ewes displaying estrus.

Effects of two oestrous synchronization protocols (Ovsynch vs double PGF2α injection) on oestrous activity, characterization of the ovulatory wave and fertility were studied in ewes during the breeding season. The Ovsynch-treated ewes (GPG-group, n = 14) received a GnRH analogue (4 μg buserelin; i.m.) followed by a PGF2α analogue (10 mg dinoprost tromethamine; i.m.) on day 7 and a second injection of a GnRH analogue 48 h later. The double PGF2α-treated ewes (2PGF-group, n = 14) received a double injection of a PGF2α analogue (10 mg dinoprost tromethamine; i.m.), 11 days apart. Follicular dynamic was ultrasonographically monitored for four consecutive days, starting at the day of the last PGF2α treatment in both groups (day 0). Oestrous response and fertility traits were also recorded. The total number of follicles and the number of small follicles did not differ between the two regimes, while the number of medium follicles increased (P = 0.05) in the 2PGF-group. During four consecutive scanning days (0, 1, 2 and 3), the number of the large follicles increased significantly in both groups from day 0 to day 2. This increase continued until day 3 in the 2PGF-group, whereas it decreased sharply in the GPG-group. Oestrous rate and time to onset of oestrus were lower (P < 0.05 and P = 0.1; respectively) in the GPG-group (42.85%; 34.0 ± 2.1 h) than in the 2PGF-group (78.57%; 50.4 ± 7.3 h). Treatment with GPG-protocol reduced (P < 0.05) the interval from the second PGF2α treatment to ovulation compared with the 2PGF-protocol (85.8% of ewes ovulated within 60.0 ± 3.1 h vs 78.6% of ewes ovulated within 84.4 ± 3.1 h). Conception rate and litter size did not differ between the two regimes. In conclusion, a tighter synchrony of ovulation could be obtained following application of Ovsynch-protocol in sheep.