Utilization of dl - and l -tryptophan in young pigs

Two trials involving young pigs (total numbers 288 and 400, respectively) were performed to compare the biological activity of Dl- and L-tryptophan under restricted (trial 1) and ad libitum (trial 2) feeding conditions. In trial 1, three additions of Dl-tryptophan (0·3, 0·6 and 0·9 g/kg) and two additions of L-tryptophan (0·3 and 0·6 g/kg) to a basal diet containing 0·9 g natural tryptophan per kg were tested. In trial 2, the treatments were additions of 0·4, 0·8 and 1·2 g Dl- or L-tryptophan per kg to a basal diet having 1·3 g natural tryptophan per kg. Both trials were of 6 weeks duration. In trial 1, almost equal performance was achieved with both tryptophan sources at a dietary level of 0·3 g/kg, whereas at a level of 0·6 g/kg, Dl-tryptophan produced slightly better performance in weight gain, food intake and food conversion efficiency than did L-tryptophan. In trial 2, the supplemental level of 0·4 g L-tryptophan per kg produced weight gain and food intake results which were significantly superior to those of Dl-tryptophan. However, at supplemental levels of 0·8 and 1·2 g/kg, diets with Dl-tryptophan produced somewhat better performance than did L-tryptophan. Based on the results of trial 2, it was estimated that the pig's need for total tryptophan over the weight range of 10 to 35 kg is at least 2·3 g/kg in a diet having 10·3 MJ net energy per kg. © 1988, British Society of Animal Science. All rights reserved.