The Effect of Gonadotrophin Releasing Hormone and Follicle Stimulating Hormone in Conjunction with Pregnant Mare Serum Gonadotrophin on the Superovulatory Response in Crossbred Sheep In India

Thirty-two mature crossbred (Fine Wool Synthetic, FWS) sheep developed for fine wool production in India were treated for superovulation and oestrus synchronization in spring season. The ewes were randomly allocated to four treatment groups in a factorially designed experiment. For induction of superovulation, pregnant mare serum gonadotrophin (PMSG) was administered alone (group 1), in combination with gonadotrophin releasing hormone (GnRH) (group 2) or with follicle stimulating hormone (FSH) (group 3) and with both (group 4). Oestrus was synchronized in all the ewes by two injections of prostaglandin F2 (PGF, 10 mg each) administered at an interval of 10 days. Superovulation treatment started 48 h prior to the second PGF injection. The proportion of ewes in oestrus did not differ significantly (p>0.05) in the four groups. The use of GnRH set the ewes into oestrus earlier than the ewes in the other groups. Treatment with PMSG (800 IU) in conjunction with 4 g of Buserilin (GnRH) increased the ovulation rate (9.1±2.6 corpora lutea (CL)) above that observed when PMSG was used alone (3.0±0.7 CL). The use of FSH (0.5 U ovagen) in conjunction with PMSG was characterized by a decrease in the proportion of ewes with 2 CL (4/8 vs 7/8; p<0.05) and in the number of ovulations, i.e. CL observed (2.4±0.6 vs 9.1±2.6), and a nonsignificant increase in the incidence of large follicles (LF) (4.6±1.28 vs 3.25±0.6; p>0.05). The interaction between treatments of FSH and GnRH was not significant (p>0.05).It is concluded that use of GnRH, in conjunction with either PMSG alone or PMSG plus FSH treatment, advanced the onset of oestrus and increased the ovulation rate in FWS sheep.