A flock of 285 Boarder Leicester x Merino ewes was allotted to two groups. For one month, one group was grazed on a high plane of nutrition and the other on a low plane. The nutrition of the groups was then inter-changed and mating commenced 10 days later. One group was decreasing in liveweight and the other increasing in liveweight throughout the mating period. In the two groups, the mean liveweights of ewes at the time each ewe first mated, were similar. Approximately half of the ewes of each

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... group underwent laparotomy and ovulation rates were recorded. All ewes were lambed in a drift system. All analyses were of data obtained from first service. The rising plane of nutrition did not result in a siginficantly higher ovulation rate than the falling plane. However, the rising plane of nutrition resulted in a significant increase in both the percentage of ewes lambing (79 per cent v. 63 per cent) and in the number of lambs born per ewe mated (1.15 v. 0.83) or per ewe lambing (1.46 v. 1.32). Embryonic survival was lower in the group of ewes which lost liveweight. This effect was due to more severe embryonic loss in the twin ovulators within this group.