Quantitative Aspects of D- and L-Tryptophan utilization by the Young Pig

Two assays involving weanling pigs were performed to determine the biological activity of D-tryptophan. A basal diet containing 17.5% protein from corn and gelatin was supplemented with graded levels of either L- or D-tryptophan such that the regression of gain on supplemental tryptophan intake could be established. In Assay 1 wherein pigs were individually fed, a biopotency close to 60% was established for D-tryptophan. This value was checked and confirmed under ad libitum group-feeding conditions in Assay 2. The linear portion of the L-tryptophan growth curve was also confirmed in Assay 2. Weight gain plateaued at 0.121% dietary L-tryptophan. Thus, expressed as a percent of the dietary protein, a requirement of 0.69% L-, 0.86% DL- or 1.15% D-tryptophan was calculated, based on the observed biological activities for L-, DL- and D-tryptophan of 100, 80 and 60%, respectively.