Tryptophan Requirements of 5- to 15-Kg Pigs with Semipractical Pig Starters

Two 28-day trials, each using 35 baby pigs initially weighing about 5 kg and 3 weeks of age were used to determine responses in pig weight gain, feed:gain, plasma-free tryptophan and plasma urea nitrogen to graded levels of dietary tryptophan. In experiment 1 the tryptophan requirement was estimated to be about .15% of the diet in an 18.8% crude protein diet containing .103% tryptophan from feedstuffs and additions from synthetic L-tryptophan. In experiment 2 the estimated requirement also was .15% in a basal diet similar to that of experiment 1, with tryptophan additions from a delactosed whey product. Chemically determined tryptophan in delactosed whey was completely available by bioassay.