Efficacy of Supplemental Tryptophan, Threonine, Isoleucine and Methionine for Weanling Pigs Fed a Low-Protein, Lysine-Supplemented, Corn-Sunflower Meal Diet

Two experiments were conducted with weaned pigs to evaluate the efficacy of supplemental tryptophan, threonine, isoleucine and methionine in a lysine-fortified, 12% protein, corn-sunflower meal diet. A 16% protein, cornsunflower meal diet was included as a positive control. Both diets were supplemented to be isolysinic and to provide a level of lysine approximately 10% above National Research Council recommendations. Average initial weight of the pigs was 24 and 9 kg and the diets were fed for 28 and 35 d in Exp. 1 and 2, respectively. The addition of either tryptophan or threonine alone to the lysine-fortified, low-protein diet did not affect rate of gain or feed efficiency. However, the simultaneous addition of tryptophan and threonine resulted in improved (P<.05) weight gain and feed efficiency with performance equal to that of pigs fed the 16% protein diet. Further supplementation of this diet with isoleucine and methionine, in that order, had no effect on pig performance. The results suggest that the most limiting amino acids for growing swine in a lysine-supplemented, 12% protein, corn-sunflower meal diet are tryptophan and threonine. Blood urea N data supported this finding.