The effect of liveweight and liveweight change on ewe ovulation rate at 3 successive oestrous cycles

Abstract

Ovulation rate and fasted liveweight were recorded at 3 successive oestrous cycles on groups (n = 50) of Romney ewes offered daily herbage allowances of 1–10 kg DM/ewe for 56 days from 15 March 1979, and 58 days from 11 March 1980. In 1979, ewes were 53.4 kg liveweight at the start of the experiment. In 1980, lax and restricted pre-experimental feeding generated heavier (56.5 kg liveweight) and lighter ewes (51.6 kg liveweight) respectively. Ovulation rate was related to live-weight change, with a common response for the 3 categories (1979, light 1980, heavy 1980) at each successive oestrous cycle of 0.10, 0.13, and 0.08 per 100 g/day liveweight change after the start of experimental feeding. The seasonal change in ovulation rate averaged an increase of 0.12 between successive oestrous cycles and was less pronounced in groups which had had high liveweight gains. Liveweight gain increased with increasing herbage allowance, the magnitude of this response declining as the experiment proceeded. Initial liveweight gains were less for heavier than for lighter ewes.

Keywords:

• sheep, ewes
• ovulation rate
• seasonality
• liveweight
• liveweight change
• pasture feeding