Determination of the Optimum Dietary Proportions of Lysine and Tryptophan for Growing Pigs Based on Growth, Food Intake and Plasma Metabolites

Weanling crossbred pigs were divided into 24 groups and fed one of three levels of lysine and one of eight levels of tryptophan in a 3 × 8 factorial design to determine the optimum dietary proportions of these two amino acids. Weight gain and feed efficiency, and changes in plasma levels of lysine, tryptophan and urea were the response criteria. The tryptophan “requirement” and the optimum lysine:tryptophan ratio were estimated for each of the three lysine levels. The data indicate a tryptophan requirement of 0.19% to 0.23% for the 3-week-old pig when the lysine level is adequate. For pigs of this age a lysine:tryptophan ratio of from 4 to 5 was about optimum.