Timing Ovulation in Ewes Treated with Ovsynch Protocol by Different Times of PGF2 alpha Injection during the Breeding Season

This study was carried out at Sakha Animal Production Research Station, during the period from Oct., 2009 to Sep., 2010. Forty Rahmani ewes were divided into three treatment groups: the 1st, 2nd and 3rd treatment groups were intramuscularly injected (Day 0) with 1 mL GnRH analogue followed by an intramuscular injection with 0.7 mL PGF2? 5 (G1), 6 (G2) or 7 (G3) days later. A second dose of 1 mL GnRH analogue was given on day 7 (G1), 8 (G2) or 9 (G3), and artificially insemination of treated doze was carried out 24 h later, while the 4th group represented the control ewes which were allowed for natural mating from 1st to the end of January, the breeding season. Results show that one out of 10 ewes (10%) exhibited estrous activity in G1 versus 30% (3 out of 10 ewes) in both G2 and G3. Ewes in G1 treatment group showed highest (P < 0.05) lambing rate (60%), followed by G2 (50%) and the lowest in G3 (40%), while, lambing rate of the controls was 60%. Litter size and fecundity were significantly the highest (P < 0.05) in G1 (1.67/litter and 100.2%), followed by G2 (1.40/litter and 70%) and the lowest in G3 (1.25/litter and 43%), respectively. P4 concentration was significantly (P < 0.05) increased in all treatment groups as affected by the 1st GnRH in-jection, thereafter, it showed marked decrease in all treatment groups post-PGF2? injection. Post-2nd GnRH injection, P4 level showed again a pronounced increase in all treatment groups. On day 21-24 post-mating, P4 level showed the highest values in all treatment groups. Based on the foregoing results, using GnRH-PGF2-GnRH (GnRH, 0 d; PGF2? 5 d later and GnRH 48 h later) protocol during breeding season can be used for synchronization of estrus and ovulation to reduce service and lambing interval of ewes in the large flocks.