摘要
Two experiments were conducted to evaluate the growth response and serum concentrations （SC） of amino acids （AA） in pigs fed wheat-based diets with either deficient, adequate or excess Lys and Thr. Previously, the standardized ileal digestibilities of AA in a basal diet were determined with five ileal cannulated pigs in a digestion trial. In experiment 1, 21 pigs （12.5±0.91 kg） were used to evaluate the effect of adding 0%, 0.69%, and 1.38% free L-Lys. The best growth response was obtained with 0.69% added L-Lys, equivalent to 1.05% total in the diet. The SC of Arg, Thr, and Val were lower （P 〈 0.05） in pigs fed the Lys adequate diet, compared to the deficient, but no further change occurred with excess Lys （P 〉 0.10）. Lys SC increased with each increment in the dietary Lys content （P 〈 0.05）. In experiment 2, 20 pigs （14.3 ± 1.57 kg） were used, and the addition of 0%, 0.14%, 0.28%, and 0.42% crystalline Thr, to the 0.69% L-Lys-supplemented basal diet, was evaluated. The best response was obtained with added 0.28% L-Thr, （0.66% total Thr）, but excess Thr reduced feed intake and growth rate. Moderate and excess levels of Yhr increased the SC of Thr, but excess reduced those of Va[ and Lys. These data show that excess Thr, but not Lys, affect the performance of growing pigs. Also, these data indicate that Val may become limiting in low protein diets with excess Lys or Thr.
