The timing of a moderate nutritional restriction in mid pregnancy and its effect on lamb birth weight and ewe gestation length

Abstract

Lamb birth weight and ewe gestation length data were collected from a flock of 300-600 parous Border Leicester x Merino ewes over 4 years, as part of a study on nutritional restriction of pregnant ewes. One half of these ewes were nutritionally restricted for a 4-week period commencing 75-95 days post coitus, in order to achieve loss of maternal liveweight and reduction in body fat score to a minimum of 3. The remaining ewes with no nutritional restriction were >6 kg heavier and had a body fat score >0.8 higher at the end of the restriction period. Nutritional restriction affected (P<0.05) birth weight of lambs. With each day's delay in commencing restriction, from day 75 to day 95, gestation length was increased (P<0.001). For each additional day in utero, birth weight was increased by 40-50 g. Restriction and refeeding produced lambs of birth weights and weaning weights indistinguishable from the control ewes, and since there were no apparent disadvantages, mid pregnancy restriction is an alternative nutritional strategy for pregnant ewes.