The effects of different dietary protein levels were measured with a comparative slaughter technique. Body composition and protein and fat excretion were measured in various body component in Yorkshire gilts. Eight gilts were slaughter at 20 kg at the beginning of the experiment to determine the initial body composition. 3 groups of 24 gilts were assigned different diets for the growth period 20 to 55 kg ( one group fed on a 16.6 % crude protein (CP), and the 2 others 15.0 and 13.0% CP respectively). 8 gilts from each group were slaughter at this time (55 kg) to verify body composition. For the finishing period, the CP was reduced by approximately 2% on each diet and the remaining gilts were slaughter at 100 kg. The CP levels did not affect the carcass retail cuts, except for smaller trimmed ham for the gilts fed 13% and 11% CP diets. For the same group of gilts, the fat content of the empty body and in the carcass was the highest and the water accretion was the lowest. No effect of the level of crude protein could be observed for the chemical body composition, the protein and fat accretion rates, and the estimated lean yields.

This experiment verified the effect on different crude protein concentration on the body composition of gilts. The results showed that difference noticed for the lowest crude protein diet (13% crude protein in the diet for growing period and 11% for the finishing) were on the smaller size of the trimmed ham, highest fat content in the empty body and lowest water retention rate. Reduced protein corn/soybean meal based diets supplemented with amino acids, for the growing (13% CP) and finishing (12,8% CP) stages, does not affect the body composition, the estimated carcass lean yield, and the nutrient deposition rate for pigs that have a better potential than average for lean growth.