1. Nine groups of 4 litter-mate Wessex Saddleback gilts were divided on a within-litter basis between 4 treatments so that they were reared from 8 weeks of age to 200 1b. live-weight according to different levels of total feed intake; (a) a high level rising to 8·0 1b. meal per day at 200 1b. live-weight, (b) a medium level approximately 80% of the high, (c) a low level approximately 60% of the high and (d) changing from the low to the medium level between 14 and 16 weeks of age. From 200 1b. live-weight to mating at first heat after reaching 300 1b. all were fed to the medium scale (6·5 1b. meal per day), and all were treated alike during each of 3 pregnancies and lactations.
2. Mean rate of growth from weaning to 100 1b. and from 100 to 200 1b. differed significantly between treatments (P<0·001), and mean efficiency of feed conversion of the low-plane group was significantly poorer than that of the high-plane group (P<0·05) from weaning to 100 1b. live-weight.
3. All gilts, regardless of treatment, reached puberty at approximately the same age (25 weeks), with the result that mean weight at puberty differed markedly between treatments (P<0·001); 116, 154, 189 and 147 1b. for treatments (a) to (d) respectively.
4. Gilts reared on medium and high planes of feeding exhibited oestrus less strongly than those reared on the low-plane, with the result that mean weight at successful mating was significantly greater in these two groups (P<0·05).
5. Four gilts in the low-plane group and one in the high-plane group failed to conceive after repeated matings, but numbers were insufficient to indicate the significance of this.
6. From the original 36 gilts, 27 first litters, 26 second litters and 25 third litters were produced and reared to 8 weeks of age. There was no significant difference between treatment groups in litter size at birth, mean weight of piglets at 3 or 8 weeks of age or total litter weight at weaning.
7. Trouble from temporary collapse of the legs was experienced in all but one gilt of the high-plane group between 6½ and 7½ months of age.