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Tryptophan and Threonine Requirements of Young Pigs and Their Effects on Serum Calcium, Phosphorus and Zinc Concentrations¹

South Dakota State University, Brookings 57007

Abstract

Four 28-d trials were conducted using a total of 432 pigs, with average initial weight across trials ranging from 6.3 to 9.7 kg, to estimate the tryptophan (trials 1 and 2) and threonine (trials 3 and 4) requirements of pigs fed low protein, corn-sunflower meal diets. The effect of tryptophan, threonine and protein level on serum calcium, phosphorus and zinc also was studied. The diets contained either 12 or 13% protein and were calculated to be adequate in all nutrients except crude protein and the amino acid being investigated. A lysine supplemented, 18% protein, corn-sunflower meal diet was included in all trials as a positive control. In trial 1, weight gains of pigs increased linearly (P<.005) while feed conversion improved cubically (P<.05) as dietary tryptophan increased from .14 to .22%. Pigs fed the 18% protein diet gained faster (P<.05) and required less feed/gain than pigs fed low protein diets. In trial 2, weight gains improved quadratically (P<.005) and feed conversion improved linearly (P<.05) as dietary tryptophan increased from .104 to .204%. Serum phosphorus and zinc concentrations were lower (P<.05) in pigs fed the 18% protein diet. In both trials, serum urea N responded quadratically (P<.05) to increasing dietary tryptophan, and was lower (P<.05) in pigs that were fed diets supplemented with L-tryptophan than in those fed the low protein basal or 18% protein diets. Weight gains increased linearly (P<.05) and feed conversion improved linearly (P<.005) in trial 3 while serum urea N, daily gains and feed conversion improved cubically (P<.005) in trial 4 with increasing levels of dietary threonine. Serum urea N was lower (P<.05) in pigs fed diets containing supplmental L-threonine. Serum phosphorus and zinc were lower (P<.05) in pigs fed the 18% protein diet than in pigs that were fed all 12% protein diets. The results indicate that the minimum dietary threonine requirement of the young weaned pig (8 to 21 kg) is approximately .63%, while the minimum dietary tryptophan requirement of the 6- to 22-kg pig is approximately .16%.

¹ Published with the approval of the Director of the South Dakota Agr. Exp. Sta. as Publication No. 2179 of the Journal Series.

² Dept. of Anim. and Range Sci.

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