1. Forty-five Friesian first calf heifers were used in an experiment to study the effect on milk production of two levels of feeding in the last 6 months of pregnancy and two levels of feeding in the first 8 weeks of lactation.

2. In each of two years herbage was rationed daily at different rates to two groups of pregnant heifers from late April until they calved in the autumn. The mean daily rations were 3·5 lb herbage dry matter and 2·4 lb herbage dry matter per 100 lb live weight for the two groups. The mean daily amounts consumed were 2·1 and 1·8 lb herbage dry matter per 100 lb live weight respectively.

3. The rates of gross live-weight gain during the period April to August were 2·2 and 1·7 lb/day for the two groups respectively. Estimated as the net gain of the dam alone, the rates of live-weight increase during the experimental period were 0·89 and 0·49 lb/day respectively, amounting to a mean difference in live weight after calving of 57 lb between the groups.