MARGINAL EFFICIENCY OF FREE OR PROTECTED CRYSTALLINE L-TRYPTOPHAN FORTRYPTOPHAN AND PROTEIN ACCRETION IN EARLY-WEANED PIGS

We conducted an experiment to determine the efficiency of dietary tryp tophan (Trp) for protein and Trp accretion in 4-kg (live weight) pigs. Five Trp-deficient diets were fed for 18 d after weaning. The basal d iet contained 23.4% protein and .14% Trp. The four other diets were si milar to the basal diet but were supplemented with .06 or .12% free or protected crystalline Trp. No differences were found between the two crystalline Trp forms for all variables under study. Equal amounts of all diets were fed by intragastric tube feeding. Daily weight gain (P <.10), gain:feed (P <.05), and daily protein retention (P <.01) increa sed linearly as dietary Trp increased. Similarly, retention and gross efficiency (retained: intake) of almost all amino acids increased. Try ptophan retention also increased linearly (P <.05),but gross efficienc y was maximal (40.1%) with protein-bound Trp from the basal diet, and it decreased linearly as dietary Trp increased. This important reducti on was the result of a low marginal efficiency for crystalline (13.6 /- 3.3%) free or protected Trp.