Effect of GnRH and hCG injection on the reproductive performance and serum progesterone concentration of ewes during spring season

This study was carried out to investigate the effect of different hormonal programs on the reproductive parameters and serum progesterone concentration of Lake-Ghashghaei ewes in spring season. In this study, 144 ewes were selected from two large nomadic herds. The ewes were synchronized using progesterone sponges. One day before harvesting the sponges, all ewes were injected intramuscularly with 400 IU of eCG. Then ewes were divided into six groups (12 ewes). In the first herd, 1 (GnRH-1 group), 2 (GnRH-2 group), 5 (GnRH-5 group), 7 (GnRH-7 group) and 12 days (GnRH-12 group) after estrus observation, 25.00 µg GnRH was injected intramuscularly to the ewes. In the second herd, the ewes were received 500 IU of hCG on days 1 (hCG-1), 2 (hCG-2), 5 (hCG-5), 7 (hCG-7) and 12 (hCG-12). In each herd, a group of 12 ewes received only eCG and progesterone sponges and was considered as control group. The results showed that twinning rate, the number of born lambs, fecundity and prolificacy rate were higher GnRH and hCG received groups on the second day compared to other groups. The serum progesterone concentration was significantly higher in all groups received GnRH and hCG compared to control group. In general, the results showed that GnRH and hCG two days after mating improved different reproductive activities in addition to increasing serum progesterone concentration. On the other hand, hCG had a greater effect on progesterone concentration, the number of born lambs and the fecundity rate compared to GnRH.