Fifty-two Large White gilts, arranged in thirteen groups of four litter sisters, were allocated at mating to one of four treatment groups. These treatments, arranged as a 2 × 2 factorial, allowed daily energy intakes in pregnancy of 8·3 Meal (H(e)) or 5·2 Meal (L(e)) and of average daily intake during lactation of 20 Meal (h(e)) or 13·8 Meal (m(e)). Daily intakes of protein, minerals and vitamins were similar for all treatments. There were no consistent differences in health or breeding regularity between the treatments.

The H(e) sows had a net gain in pregnancy 22 kg greater than the L(e) sows. Feeding the higher level in lactation (h(e) resulted in a reduced sow weight loss during lactation of 20, 12 and 10 kg in the first, second and third parities respectively, as compared with the m(e) sows. There were no consistent effects on the numbers of pigs born apart from the first litter in which L(e) sows produced significantly larger litters at birth. The higher energy intakes in pregnancy and lactation led to very similar increases in the weights of the piglets, of the order of 0.1 kg at birth, 0.4 kg at 3 weeks of age, and 1.1 kg at 8 weeks of age. Sowsgiven the same overall energy intake throughout their reproductive life (H(e) m(e), L(e) h(e)) at the end of the third litter had similar live weights and had produced a similar total weight of weaned pigs. The practical implications of these results are discussed.