Eight replicates of four Large White littermate female pigs were used to evaluate the effect of
protein and lysine levels in the diet on the efficiency of protein and energy utilization. In each
replicate, one pig was slaughtered at about 20 kg live weight and the others received three diets
that contained (per Meal digestible energy) 37.5 and 2.00 g (diet pl), 37.5 and 2.35 g (diet pL) or
45.0 and 2.35 g (diet PL) of digestible protein and lysine, respectively. Pigs were slaughtered after a
7-wk period. Tissue and chemical composition of the gain and energy and nitrogen gain were
determined by using the comparative slaughter technique. Metabolizable energy (ME) intakes were
similar in the treatments. Pigs fed the pl diet had a smaller body weight and muscle gain and
retained less nitrogen and more lipids than pigs fed pL and PL diets. The decrease in the level of
nonessential nitrogen in the diet (pL vs PL) did not affect body weight and muscle gain and the
amount of nitrogen retained in muscle tissues. However, pigs given the PL diet had a higher total
nitrogen retention and a lower fat deposition and exhibited a higher heat production. For each
gram of additional protein catabolized for energy purposes (PL vs pL), heat production was increased
by 1.8 kcal. The amount of lysine per unit of muscle gain (38 g/kg) or protein deposited
(120 g/kg) was independent of protein and lysine levels in the diet. Estimates of energy (indirect
calorimetry) and nitrogen (balance technique) retention were also obtained on the same animals;
results were comparable with data obtained by direct measurements