Litter size and milk yield have been significantly increased in modern genotypes and gilts are now lactating at a stage when they still have the potential for substantial maternal lean tissue growth. Voluntary intakes are seldom adequate to meet the nutrient requirements for lactation, and catabolism of body tissue occurs. It is possible that higher ratios of ideal protein to energy are desirable in the first lactation to balance the energy contributed by fat catabolism. This possibility was tested in a controlled experiment.

The study was conducted in a large commercial herd with Large White (LW) and Landrace (LR) first cross sows which had been mated to LW, LR, LW x LR and Duroc boars. Three lactation diets were formulated, one being close to current recommendations for modern, high producing sows (Diet A) while diets B and C had, respectively a 9 and 33 percent higher ratio of lysine to digestible energy. The diets were based mainly on cereals (barley and wheat), both extracted and full-fat rape seed meal, soya bean meal and biscuit meal. The calculated nutrient content of the diets is presented in Table 1.