Tryptophan, Threonine, Isoleucine and Methionine Supplementation of a 12% Protein, Lysine-Supplemented, Corn-Soybean Meal Diet for Growing Pigs

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Abstract
Five experiments were conducted to assess the value of supplemental amino acids (tryptophan, threonine, isoleucine and methionine) in a lysine-fortified, 12% protein, corn-soybean meal diet for growing pigs (18 to 35 kg). Methionine, as methionine hydroxy analog, was included in the basal diet in all experiments except one, in which the need for supplemental methionine was evaluated. The low protein, basal diet was supplemented with .3% lysine to provide a level equivalent to that in a 16% protein, corn-soybean meal diet. The basal diet was calculated to contain .14% tryptophan, while analyzed levels ranged from .13 to .15% tryptophan. The addition of tryptophan alone (.015 to .045%) to the lysine-methionine fortified basal diet failed to improve growth rate, efficiency of feed utilization or N retention. Similarly, threonine supplementation (.1%) of the basal diet did not affect performance. However, the combination of .04% tryptophan and .1% threonine significantly improved growth rate and feed:gain ratio to a level equivalent to that of pigs fed the 16% protein, positive control diet. Supplemental isoleucine (.1%) in the presence of added tryptophan or tryptophan and threonine was without effect. In the experiment in which the need for methionine supplementation was evaluated, methionine addition (.1%) to the lysine-fortified basal diet improved growth rate, but not feed efficiency. Methionine had no effect on the response to either threonine or tryptophan addition. A titration experiment indicated that supplementation of .03% tryptophan to a lysine-methionine-threonine fortified basal diet supported optimal growth rate and feed efficiency of pigs. The results suggest that the growing pig (18 to 34 kg) allowed to consume a corn-soybean meal diet ad libitum requires approximately .17% total tryptophan (.13% available tryptophan) for optimal performance. Copyright © 1983. American Society of Animal Science. Copyright 1983 by American Society of Animal Science.

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