Two experiments were carried out to evaluate the effect of five digestible threonine:lysine ratios (TL) on the nitrogen balance of growing pigs and five levels of net energy (NE) on growing-finishing pigs performance. In the first experiment, 15 high-lean commercial crossbred barrows, with initial weight of 37.0 ± 2.6 kg, were allotted to a completely randomized design, with five diets (digestible threonine:lysine ratio of 0.574, 0.624, 0.673, 0.722, and 0.772, in low protein diets, 14.7%) and three replications. Absorbed crude protein (ACP) and plasma urea nitrogen (PUN) showed a quadratic effect and the best threonine:digestible lysine ratio was 0.658 (mean of ACP and PUN). In the second experiment, five EL dietary levels were evaluated with digestible threonine:lysine ratio of 0.658. Forty pigs (20 barrows and 20 gilts) with 30.2 ± 1.3 kg were allotted to a completely randomized design, as a 5 × 2 factorial arrangement, composed of five levels of NE (2.410, 2.450, 2.490, 2.530, or 2.570 Mcal/kg) and two sexes, with one animal per cage. In the finishing phase and total period, increasing NE levels reduced feed intake (FI), improved feed:gain ratio (FGR) and increased fat deposition. Digestible threonine:lysine ratio of 0.658 improves nitrogen retention and the increasing net energy levels decrease FI and improve FGR, but may increase fat deposition in pigs.
carcass; energy; ideal protein; nitrogen balance; performance
