Dietary tryptophan need of broiler males from forty-two to fifty-six days of age.

Tryptophan requirements of broiler males from 42 to 56 d of age were studied. Ross x Ross 308 chicks were placed in an open-sided house, and provided common starter and grower diets from 0 to 42 d of age. Subsequently, a corn, soybean meal, corn gluten meal, and gelatin combination of feedstuffs provided 0.12% Trp to which 0.04% increments of L-Trp were supplemented at the expense of an isonitrogenous amount of L-Glu to 0.24%. Birds that received diets containing 0.12% Trp exhibited aberrant behavior based on the spillage of considerable amounts of feed from the trough and contamination of adjacent waterers with floor litter. There were reductions in body weight gain, feed conversion, and carcass and breast fillets weights and yields with dietary Trp at 0.12%, but these were not affected at Trp levels at or above 0.16%. Exponential regression analyses showed that body weight gain improved as Trp increased, with maximum overall performance being attained at 0.17%, whereas chilled carcass weight maximized at 0.16% dietary Trp. Nitrogen retention measured using the same experimental feeds and sample birds at 48 to 49 d of age was unaffected by dietary Trp. Plasma uric acid, albumin, total protein, and aspartate-transferase measured concurrently with nitrogen retention were not altered; however, blood glucose was reduced in broilers fed 0.12% dietary Trp. Overall results suggest that broiler males need approximately 0.17% dietary Trp between 42 and 56 d of age, which closely agrees with the NRC (1994) recommendation of 0.16% Trp estimated from modeling for this feeding period.