The Effect of GnRH Given on Day of Mating on Ovarian Function and Reproductive Performance in Lohi Sheep

The present study was conducted to investigate the effects of GnRH (Dalmeralin) treatment given on the day of mating on reproductive performance in Lohi sheep. Seventy six ewes 3-5 year old, weighing 44 ± 0.4 Kg were put to rams at synchronized estrus using two intramuscular injections of 2 ml PGF2a analogue (Dalmazin) 11 days apart. These animals were divided into two equal groups through random stratification by body weight and were given either saline (group 1) or 2 ml GnRH (group 11) on day of mating. A total of 16 ewes were slaughtered on day 25 of pregnancy (eight ewes from each treatment group). GnRH administration on the day of mating increased (P<0.01) plasma progesterone concentration compared to control. There was a tendency for a higher non-return rate and a lower number of ewes returned to estrus in the GnRH treated ewes, but the difference between the two groups was non significant (P>0.05). Pregnancy rate was higher in GnRH treated group (83.3%) than control (60%) group (P<0.05). The ewes in GnRH administered group had more twins (P<0.05) than those in control group (28 v 10). In conclusion, GnRH administration improved reproductive performance of ewes when administered on the day of mating, probably through its beneficial effect on embryo survival by enhancing luteal function