Lysine Imbalance of Corn Protein in the Growing Pig

Three trials were conducted with 198 growing pigs to evaluate amino acid additions to a fortified corn diet. Lysine supplementation at 0.2% of the diet caused a marked depression in voluntary feed intake and rate of gain. The same level of supplemental methionine was without effect. Supplemental DL-tryptophan at 0.05% of the diet completely overcame the depression caused by lysine. The data suggest that tryptophan is the first-limiting and lysine the second-limiting amino acid in corn protein and that methionine is not third-limiting. Pigs fed corn diets on pasture performed better than those fed in drylot, particularly when supplemental tryptophan was not provided.