| The effect of amino acid restrictions during the grower phase and selection for lean growth efficiency on pig performance, serum profile, carcass traits and meat quality, and the effect of amino acid restrictions during the grower phase on nitrogen (N) balance were investigated in three studies.;In the first study, the effect of selection for lean growth efficiency was assessed. The select line (SL) pigs grew faster and more efficiently ( P < 0.05) than the control line (CL) pigs during the grower and finisher 1 phases. The SI, pigs had less ultrasound backfat (P < 0.05), lower serum urea N (P < 0.05) and leptin concentrations, heavier internal organs (P ≤ 0.05), superior carcass characteristics (P ≤ 0.10), higher (P < 0.01) estimated daily lean gain and improved lean growth efficiency (P < 0.01), and lower meat quality scores (P < 0.05) than the CL pigs.;In the second study, pigs from the same SL and CL were used to determine the effect of dietary lysine content (5.0, 7.0, 9.0, or 11.0 g lysine/kg) during the grower phase and genotype on pig performance. Pigs were fed common finisher 1 and finisher 2 diets. Following a growth depression, previously restricted pigs grew faster and utilized feed more efficiently (Ln, P < 0.05) during the subsequent phases than those fed adequate grower diets. Generally, there was no effect of grower diet on overall growth performance or carcass and meat characteristics. There was no grower diet x genotype interaction in the response criteria of interest, indicating that restricted pigs compensated fully regardless of genotype.;In the third study, crossbred castrated male pigs were used to investigate the effect of grower diet (5.0 vs 1.1 g/kg lysine) on pig performance and N balance. Pigs were fed common finisher 1 and finisher 2 diets. Pigs fed the low-lysine diet grew slower and less efficiently (P < 0.001) than those fed the high-lysine diet. Generally, there was no effect of grower diet on growth performance during the grower-finisher phase and carcass characteristics, indicating a complete compensation. After a growth depression, previously restricted pigs grew more efficiently (P < 0.05), excreted less (P < 0.05) urinary N, and retained more dietary N (P < 0.05) compared with the non-restricted pigs.;These results indicate that selection for lean growth efficiency was effective in changing the growth rate, metabolic and hormonal profile, and body composition of the SL pigs. Although the SL pigs had superior growth performance and carcass quality, pigs responded similarly to the early dietary restrictions and compensated completely regardless of genotype. In addition, the restricted pigs utilized feed more efficiently and exhibited compensatory N retention, which can have a positive impact not only on the overall efficiency of pig production but also on the environment by reducing the excretion of unutilized N. |
