Selection for the reduction of carcase fat and the promotion of lean tissue growth has resulted in the production of faster growing, genetically lean breeding females. These animals often have very limited body fat reserves to utilise at times of high nutrient demand, such as during lactation. It is possible that reproductive performance and longevity may be improved as a consequence of alteration of the body composition of the breeding female by nutritional means.

The experiment was designed to investigate the consequences for genetically lean animals of restricting lean tissue growth and promoting fat deposition in the period prior to a maiden service and in gestation using a low protein diet, and minimising fat loss in lactation using a nutrient dense diet (Treatment E) in comparison with feeding a conventional single diet (Treatment C). Two hundred and forty purebred Large White and Landrace gilts were allocated to one of these two nutritional regimes at 6 months of age on the basis of breed, liveweight and backfat. Animals remained on treatment for three parities and growth and performance parameters were monitored.