Effects of GnRH agonist (CinnaRelin) on reproductive performance in synchronized Iranian crossbred ewes during the breeding season

Abstract

This study was carried out to investigate the efficiency of GnRH on reproductive performance of synchronized Iranian crossbred ewes during the breeding season. The ewes (n = 90) were treated with CIDR containing 30 mg progesterone for 14 days and were injected with 400 IU PMSG at the time of removal of the CIDR. The ewes were then divided into three equal groups of 30 ewes each. One milliliter of water soluble was administered to each ewe in the Group 1 (control) at the time of both the CIDR withdrawal and AI. In the group 2 approximately 12.5 µg of GnRH (CinnaRelin) were injected to each ewe immediatly after AI. In the 3 Group, 12.5 µg GnRH were injected to each ewe on 11 to 13 days post-insemination. Intracervical AI with diluted fresh semen was performed once at 12 hours following the estrus onset. Lambing and multiple birth rates were significantly higher (P<0.05) in the Group 2 (123.3 % and 45.8 %) in comparison to other groups. Pregnancy and fecundity rates tended to be higher in the Group 2 (80 % and 154.2 %) and the Group 3 (76.6 % and 130.4 %), when compared with the control Group (66.6 % and 110 %). However, the differences among any groups in terms of the number of twin lambs, gestation period, lambs birth weight and male and female lamb rate were statistically insignificant (P>0.05). In conclusion, GnRH administration improved the reproductive performance of the ewes when administrated at the time of AI or during the midluteal phase after AI.