The effect of different times of GnRH injection on reproductive performance of Lake-Ghashghaei ewes supperovulated with eCG in nomadic breeding condition

In order to investigate the different times of GnRH injection on the reproductive activities of Lake-Ghashghaei ewes supperovulated with eCG in autumn season, 60 ewes (2-3 ages and average body weight 49±1.8 Kg) were chosen. Estrus cycle of ewes were synchronized by progesterone sponges during a 14 days period. One day before removing the sponges, 400 IU of eCG were injected intramuscularly. Then the ewes were divided into 4 groups according to receiving GnRH on different days (one, seven and 12 days) or not receiving GnRH (control) after estrus observation and reproductive indexes such as the rate of return to estrus and pregnancy rate, were measured and compared among different groups in two continuous estrus cycle. The result indicated that there were not any significant differences (P>0.05) in the rate of return to estrus, pregnancy rate, parturation rate, fecundity and prolificacy among treatment groups, but the rate of twin birth was significantly (P<0.05) lesser in the groups, receiving GnRH in 7 and 12 days compared with the group that recieved GnRH in the first day. Serum progesterone concentration in pregnant, delivered, single and twin births ewes that received GnRH were significantly (P<0.05) more than control ewes. In conclusion, GnRH administration during different days after mating increased serum progesterone concentration in Lake-Ghashghaei ewes. Moreover, the rate of twining birth in ewes which received GnRH on the first day, was significantly more compared with using GnRH on 7th and 12th days after estrus.