Effects of GnRH agonist (CinnaRelin) on reproductive performance in synchronized crossbred ewes

A completely randomized design experiment was conducted on one hundred and twenty crossbred ewes during the breeding season to investigate the efficiency of GnRH agonist (CinnaRelin) on reproductive performance in synchronized crossbred ewes. The ewes were treated with CIDR with 30 mg progesterone for 14 days and were injected with 400 IU PMSG at the time of removal of the CIDR. Hence, the animals were randomly divided into four equal groups of 30 ewes each. One milliliter of physiological saline (0.9% NaCl, placebo) was administered to each ewe in Group 1 (control) at the time of both the CIDR withdrawal and AI. Approximately 12.5 µg GnRH was injected to each ewe in Group 2 and 3, at the time of 2 h prior to AI and at the time of AI, respectively. In the 4 Group, was injected to each ewe 12.5 µg GnRH on days 11 to 13 post-insemination. Intracervical AI with diluted fresh semen was performance once at 12 h following the onset of estrus. Lambing rate and multiple birth rates were significantly higher (P < 0.05) in Group 2 (123.3% and 45.8%) in comparison to other Groups. When the number of single lambs was statistically compared only a significant difference (P < 0.05) between Groups 1 and 2. Pregnancy and fecundity rates tended to be higher in Group 2 (80% and 154.2%), Group 3 (76.6% and 130.4%) and Group 4 (76.6% and 126.1%), if compared with the control Group (66.6% and 110%). However, the differences among any of the 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, administration of 400 IU PMSG preferably upon CIDR removal is essential to obtain better fertility rates at induced estrus and following AI. Additionally, exogenous GnRH treatment at the time of 2 h prior to AI, at the time of AI and 11 to 13 days after AI increase the multiple birth rates of ewes.

crossbred ewes, lambing rate, GnRH, synchronization.