Oat, barley or triticale grain, enriched by addition of nitrogen, minerals, and an ionophore, was fed for 90 days as supplement at a level of 500 g per head per day to SA Mutton Merino ewes during late pregnancy and lactation. Data from 125 pregnant ewes were used to investigate live mass change during late pregnancy and lactation, while wool production (derived from 10x 10cm midrib squares tattooed on the right side of the ewes) was studied with 57 of these ewes. Data from 130lambs, alive on the ewes at weaning, were used to determine the influence of supplementation on birth mass, weaning mass and preweaning growth rate. The ewes receiving supplement succeeded in maintaining a higher (P ≤0,05) average live mass during lactation than the unsupplemented control group. Ewes receiving enriched barley tended to have smaller losses of live mass than those supplemented with enriched triticale. Supplementation tended to increase greasy and clean wool production per unit skin area, but no significant deviations from the control group were found. The birth mass of lambs born from ewes fed the supplement, tended to be higher than in the control group. Lambs reared by ewes supplemented with enriched oats and triticale were heavier (P ≤0,05) at weaning, with faster (P ≤0,05) growth rates than control group lambs. A similar tendency y was observed in lambs reared by ewes receiving enriched barley as supplement.