1. Four groups of three litter-sister Large White gilts were given during four successive pregnancies a daily meal allowance of either 2·70 kg (High), 1·35 (Low) or 1·35 kg for 76 days followed by 2·70 kg until parturition (Low-High). During 8-week lactation periods all received the same daily allowance of 1·8 kg meal plus 0·35 kg for each piglet suckled.

2. On the 100th day of the fourth pregnancy all sows were slaughtered. The major internal organs were weighed and measurements recorded of the length of carcass and backfat thickness at shoulder, midback and loin. The carcasses were then separated into bone, skin, subcutaneous fat and muscles plus intermuscular fat. The weights of radius-ulna, tibia-fibula, humerus and femur were recorded.

3. In each of the treatment groups the live-weight changes of the sows in the fourth pregnancy were almost identical to those in the third pregnancy.

4. The mean total carcass weights for the High, Low and Low-High sows were 154, 92 and 110 kg respectively, and the mean subcutaneous fat contents of the carcasses 14, 4 and 6 kg respectively.

5. The relative proportions of the weights of the organs to carcass weight, weight of bone to weight of muscle plus intermuscular fat, and the weight of individual bones to total bone weight were relatively unaffected by the treatments after allowance had been made for total carcass weight.

6. The implications of the changes in body composition on the lifetime reproductive performance of sows are discussed.