Study of Reproductive Performance of Crossbred Ewes Treated with GnRH and PMSG during Breeding Season

Reproductive performance was evaluated in non-lactating crossbred ewes to which were administered the exogenous GnRH and PMSG. The ewes were randomly allocated in three treatment groups (n=40). After accurate detection of estrus and 2 hours prior to mating, 2.5 mL of distilled water and 2.5 mL of GnRH were injected intramuscular to each ewe of the first (control) and second group, respectively. In the third group, the ewes were pretreated with CIDR for 14 days and received 400 IU PMSG at the time of withdrawal of the CIDR. After injection of PMSG, fixed-time artificial insemination was performed with 0.5 mL of fresh diluted semen. No significant differences were observed in term of the pregnancy, lambing, and fecundity rates between ewes treated with GnRH and control group (87.5, 97.5, and 1.114% vs. 75, 82.5, and 1.1%, respectively). Twining rate was higher in the ewes treated with GnRH than synchrony or control groups (18.18, 4, and 6.5% respectively, P<0.05). In the artificially inseminated group, pregnancy, lambing and fecundity rates were 77.5, 62.5, and 0.81%, respectively. In conclusion, the results showed that treatment of ewes with GnRH at time of estrus and prior to mating, improved the conception and twining birth rates. Also injection of PMSG after CIDR removal caused an increase in efficiency of fertility rate and shorter breeding period.