Effects of Crystalline Lysine, Threonine and Tryptophan Supplementation of Diets Containing Reduced Protein Levels on Performance of Growing Pigs

Three hundred and fifty-two growing pigs were utilized in three growth trials to investigate the effects of crystalline amino acid supplementation on growing pigs' growth performance and feed consumption. In Exp. 1, diets were formulated on the basis of digestible amino acids. Utilization of rapeseed meal plus cottonseed meal (R + C) in diet supported similar average daily gain (ADG), feed/gain (F/G) and cost per gain (p > 0.05) to group of soybean meal (SBM). In Exp. 2, 14% CP diets containing equal amount of cottonseed meal and rapeseed meal were formulated with the addition of threonine and/or tryptophan. Supplementation with threonine improved ADG and F/G (p < 0.05). Supplementation with only tryptophan made no benefits for ADG of growing pigs. In Exp. 3, diets with different threonine level were formulated. Increasing dietary threonine to 0.54% improved (p < 0.05) ADG and F/G compared to 0.45% dietary threonine. Increase in dietary threonine did not improve ADG (p > 0.05) but decreased F/G (p < 0.05) because of a decrease in average daily feed intake. Pigs fed diet with dietary threonine/lysine ratio of 67.5% supported optimum growth performance.