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In the spring of 1965, anoestrous lactating Border Leicester X Merino ewes were treated for 13 days with intravaginal sponges impregnated with 17a - acetoxy 6a - methylpregn - 4 - ene - 3,20 - dione (MAP) 7-11 weeks after lambing. Each ewe received 1000 i.u. Pregnant Mare Serum Gonadotrophin (PMSG) at the time of sponge removal. Half of the ewes received another 1000 i.u. PMSG 16 days after sponge removal. In the 2-4 days after sponge removal 80.5 per cent of the treated ewes exhibited oestrus, and 75.8 per cent of these were pregnant at autopsy 15 weeks later. The mean number of foetuses per pregnant ewe was 2.46. It was not until approximately 15 weeks after the period of treatment that a similar number of untreated ewes had exhibited oestrus. The second injection of PMSG had no effect on either the number of ewes pregnant or on the number of foetuses present at autopsy. This was largely due to the high rate of conception at the first induced oestrus.

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