Replacing protein supplements in barley-based diets for growing pigs with free lysine and methionine

Abstract

Protein metabolism and utilization, and performance were examined in pigs kept on diets with two protein levels, 15 and 17 % crude protein(cp), and supplementation with free L-lysine and DL-methionine. In the 5 x 5 Latin square balance trial, 15 and 17 % cp diets were fed with and without supplementation with 2 g lysine/kg feed and one 15cp diet with both lysine and 0.7 g methionine. The diets had 120 and 136 g DCP/FU, lysine 7.8, 9.4 and 11.0g/kg and sulphur amino acids 4.4, 5.0 and 5.1 g/kg. Nitrogen retention was 13 % higher on the 17 % cp diet than on the 15 % cp diet (P > 0.05). The lysine supplementation improved N retention by 4.3 % on the 15 % cp diet and supplementation with the two amino acids improved it by 2.5 % (P > 0.05 %). Urinary urea excretion on the 17 % cp diet was 17—12 %higher than on unsupplemented 15 % cp diet, and on the diets with amino acid supplementation it was 7—8 % lower (P < 0.05) than on the diets without. In the first feeding trial with 500 pigs, the higher-protein diet gave 7.4 % better daily gains. The diet with 15 % cp supplemented with lysine gave only 2.3 % better gains than the basal 15 % cp diet. The difference in feed conversion efficiency (FCE) between protein levels was statistically significant (P < 0.05). The second feeding trial was a comparison of 17 % and 15 % cp diets in which the lysine and sulphur amino acid levels had been equalized by supplementing the 15 % cp diet with lysine and methionine. The pigs were fed on a grower diet with 18 % cp to 50kg live weight and afterwards the experimental diets were fed separately to the gilts and castrates. The pigs grew similarly on the two diets, 783 vs. 780 g daily. The FCE was better on the lower-protein diet and lower in the gilts then the castrates. The gilts gave better carcase quality than the castrates and the lower-protein diet tended to give better carcase quality. The rather poor response to supplemental free amino acids in the present study seems to indicate limitation of inadequate supply of other amino acid.