The contribution of the conceptus to weight change in pregnant Merino ewes at pasture

Abstract

SUMMARY Seventy-nine pregnant Merino ewes grazing pasture at two intensities were slaughtered in groups at intervals from 60 days after conception to post-partum. Sixty-one nonpregnant ewes were also slaughtered. The weights of various organs including uteri and their contents were recorded and the energy content of each ewe was determined. The weight of uterine contents (conceptus) increased rectilinearly with increasing foetal age to 100 days: differences between singles and twins were not significant. From 100 days to term, the relationship was also rectilinear but the slope was greater: a more rapid increase occurred with twins than with singles (P < 0·05). The nutritional difference imposed did not affect the relationship. A regression of total energy reserve on live weight (less fleece and conceptus) was established. Differences between this relationship and those established separately for non-pregnant, pregnant and post-partum ewes were not significant. The contribution of changes in conceptus weight to live-weight changes in gravid ewes is discussed.