Influence of energy and protein concentration in the diet on the performance of growing pigs 1. Response to protein intake on a high-energy diet

Abstract

SUMMARYSixty gilts by Landrace sires out of Large White × Landrace females were allocated on the basis of litter relationship and initial weight to six treatments involving the individual feeding of six dietary protein levels, 15·5%, 17·4%, 20·2%, 22·3%, 25·3% and 27·3% crude protein (CP), at a common energy level of approximately 3500 kcal/kg DE, from 23 to 59 kg live weight. Amino acid balance was maintained relatively constant with synthetic lysine, methionine and tryptophan. There were significant increases in growth rate and efficiency of feed conversion from the 15·5% to the 17·4% CP diets and significant reductions in both from the 25·3 % to the 27·3 % CP diets. Carcass lean by dissection increased linearly (r = 0·976) and fat decreased linearly (r = −0·992) with dietary protein increment over the full range studied. As best growth performance and maximum lean content were attained at different dietary CP levels, a combined measure of daily lean deposition was calculated; this indicated that maximum rate of lean growth and efficiency of feed conversion to lean were reached on the 22·3% CP level. In terms of efficiency of utilization of nutrients, maximum retentions of both DE and DCP in the edible part of the carcass appeared to be attained on the two lowest dietary protein levels.