The Effects of eCG Injection Time on the Reproductive Performance in Shal Ewes Treated with Short-Term Synchronization Program During the Breeding Season

BACKGROUND: Estrus synchronization is a valuable tool in ewe reproductive management. OBJECTIVES: This study was performed to evaluate the efficiency and determine the best time of eCG injection in short-term synchronization program based on GnRH-PGF 2α in Shal ewes during the breeding season. METHODS: One hundred and sixty non-pregnant Shal ewes, aged 2-6 years old were selected and randomly stratified to four equal groups. 25µg Alarelin acetate (GnRH analogue) and 75µg D-cloprostenol (PGF 2α analogue) were injected to all ewes, on days 0 and 5, respectively. The first group (control) did not receive any other treatment. Groups 2 to 4 received 400 IU of eCG, 48 hours before, 24 hours before and concurrent with PGF2α, respectively. Ewes were exposed to fertile rams during 96 hours post PGF2α injection. Blood serum progesterone concentrations were measured just before PGF2α injection and 10 days later. RESULTS: No difference was observed in the first serum progesterone evaluation among experimental groups (P>0.05). However, progesterone had significantly higher concentrations 10 days after PGF 2α injection in groups 2 and 3 in comparison with groups 1 and 4 (P<0.05). Simultaneous use of eCG with PGF2α led to a higher estrus response in comparison with other groups (P<0.05). During the first day after PGF2α, a higher percentage of ewes in group 2 and 3 exhibited estrus compared with groups 1 and 4 (P<0.05). Conversely, estrus expression was higher 24-48 hours after prostaglandin injection in groups 1 and 4 than the other two (P<0.05). Thus, the interval to estrus was earlier in group 2 and 3 than groups 1 and 4 (P<0.05). No significant differences were detected in terms of conception rate, lambing rate, prolificacy and fecundity among study groups (P>0.05). CONCLUSIONS: Use of eCG in different times (48 and 24 hours before and concurrent with PGF2α) in short-term synchronization program based on GnRH-PGF2α during the breeding season can be effective on estrus indices. Regarding the diversity of sheep's masses in Iran, it seems that acceptable results may be achieved when eCG is used concurrently with PGF2α in short-term protocol.