Tryptophan requirement of the commercial hen.

An experiment was conducted to determine the Trp requirement of the commercial laying hen. A corn-soybean meal diet was used that contained gelatin, which is low in Trp. Tryptophan was the first-limiting amino acid in this diet. Methionine, Lys, Arg, Thr, Val, and Ile were added to ensure that they were not deficient. Experimental diets containing 0.0, 0.02, 0.04, 0.06, 0.08, 0.10, and 0.12% Trp were fed, and a corn-soybean meal diet served as the positive control. Egg production (EP), egg mass (EM), and egg content (EC) were significantly increased by the addition of supplemental Trp. Broken-line regression indicated that the Trp requirement for EP and EC for this experiment was 136.0 (R2 = 0.81) and 136.5 (R2 = 0.82) mg per hen per d, respectively. These hens produced 43.5 g of EC, resulting in a Trp requirement of 3.14 mg/g of EC. Therefore, assuming an output of 50 g of EC, we suggest 157 mg per hen per d as the requirement for maximum production of EC.