hCG Effects Are Related to the Day of Administration After Mating in Synchronous Estrus Induced Torki-Ghashghaei Sheep.

This study investigated the effects of hCG administration during different times after mating on the reproductive parameters of Torki-Ghashghaei sheep. In the first experiment, 75 Torki-Ghashghaei ewes and 56 ewe lambs were synchronised for 14 days. One day before withdrawing the sponges, 400 and 350 IU of eCG were injected into ewes and ewe lambs, respectively. Then the ewes and ewe lambs were divided into five and four groups, respectively, based on not receiving (control) or receiving hCG in ewes on 1.5, 2, 4 and 6 days and in ewe lambs on 1.5, 2 and 6 days after mating. The results of the first experiment showed that the rate of multiple twinning, the number of lambs born, fecundity, prolificacy and progesterone concentration in ewes and ewe lambs receiving hCG on days 1.5 and two were significantly higher than those in the other groups (p < 0.05). In the second experiment, 316 ewes and 304 ewe lambs were synchronised and received 400 and 300 IU of hCG, respectively, and were divided into two groups based on receiving hCG one day and a half (hCG-1.5) and two days (hCG-2) after mating. The results showed that multiple births in ewes were significantly higher in the hCG-1.5 group compared to the hCG-2 group. The results of this study generally showed that the use of hCG on all different days after mating increased the concentration of serum progesterone. Ewes and ewe lambs receiving hCG on days 1.5 and two had the best reproductive performance compared to the other groups. In conclusion, the application of hCG on 1.5 days after mating in Torki-Ghashghaei ewes and ewe lambs during the out-breeding season could be recommended for improving twinning rate, the number of lambs born and prolificacy rate.