A trial was carried out to determine the lysine requirements for barrows during growing phase from two genetic pig groups according to the ideal protein concept. Sixteen animals from genetic common group (GCG) were used and other sixteen ones, from the genetic improved group (GIG) were allotted in a randomized block design with four treatments two replicates and two pigs per pen. The treatments constituted of the basal diet, based on corn-soybean meal containing 0.75% of lysine and other three diets, adding increasing lysine levels to get 0.90; 1.05 and 1.20% of total lysine on diet. Synthetic amino acids (L-lysine HCl, DL-methionine, L threonine and L-tryptophan) were added to keep amino acid levels according to the ideal protein profile. For GCG (20 to 50 kg of live weight), lysine levels (LL) did not affect daily feed intake (DFI), daily weight gain (DWG) and feed conversion (FC). It was observed a quadratic effect of LL on DFI and DGW in GIG (24 to 45 kg of live weight), from 0 to 14 and from 0 to 18 days, but not through total period. There was no difference between GCG and GIG for plasma urea nitrogen (PUN). The total lysine requirement, based on ideal protein concept, of castrated growing pigs for GIG (24 to 45 kg of live weight) is 1.00%, while for GCG (20 to 50 kg of live weight) is 0.75%.
amino acid; carcass traits; performance; plasma urea nitrogen
