On calving, 40 Canadian Holstein heifers were divided into two groups which grazed the same rotationally managed pastures. One group received 4·54 kg/day of concentrates per cow more than the other. Under these conditions, the group which received the higher level of supplementation (9·1 kg/day/cow) produced significantly more milk and had a significantly higher persistency but a significantly lower butterfat percentage. In terms of the immediate margin over concentrate costs, the lower level of supplementation was most economic. However if a 33 per cent residual effect can be assumed then the higher level of supplementation was profitable.