Effect of gonadotrophin-releasing hormone aned human chorionic gonadotrophin on the response of the ewe to pregnant mare serum gonadotrophin.

An experiment was conducted to determine whether gonadotrophin-releasing hormone (Gn-RH) or HCG would reduce the proportion of unruptured follicles in the Galway ewe following a high superovulating dose of PMSG given in conjunction with a progestagen to synchronize oestrus. Forty-four Galway ewes aged 1\m=1/2\to 5 years (average wt 64\m=.\7kg) were treated with intravaginal pessaries impregnated with 30 mg 'cronolone' (Synchromate: G. D. Searle) for 14 days in early October 1973. All ewes were given 2000 i.u. PMSG (Folligon : Intervet) intramuscularly in 5 ml water at the time of withdrawal of the pessaries and were placed with raddled fertile rams. At 24 hr after removal of the pessary, the ewes were assigned to three groups and were treated as follows: Group 1\p=m-\50\g=m\gGn-RH intramuscularly in 1 ml water; Group 2\p=m-\750i.u. HCG intramuscularly in 1 ml water (Chorulon : Intervet) ; Group 3\p=m-\control(no treatment). The ewes were inspected each day at 09.00 and 16.00 hours for evidence of mating. At 4\m=1/2\to 5 days following removal of the pessaries, the ewes were either