Response to tryptophan of laying hens fed practical diets varying in protein concentration

Four experiments were conducted with White Leghorn laying hens to estimate their requirement for tryptophan for optimal egg production and other parameters. In the first two experiments, the hens were fed a 14.5% protein diet supplemented with 0, .025, .05 and .075% L-tryptophan. The first experiment was conducted for 12 wk and the second for 55 wk. In the third and fourth experiments, the influence of protein concentration on tryptophan requirement was investigated. Diets formulated to contain 14, 16, and 18% protein were supplemented with 0, .02, .04, .06, or .08% L-tryptophan. Protein concentration in Experiment 3 was increased by increasing only soybean meal; in Experiment 4, it was increased by increasing all protein concentrates, resulting in the same ratio of tryptophan to protein. These experiments were conducted for 6 wk. Rate of egg production was significantly improved by tryptophan supplementation in Experiments 1 and 2, but production was inferior to that expected for commercial laying hens. The estimated tryptophan requirements were .137% of the diet and 123 mg/day per hen in Experiment 1 and .118% of the diet and 95 mg/day per hen in Experiment 2. Egg production was significantly increased by adding tryptophan to the 14% protein diet in Experiment 3 but not to the higher protein diets. The estimated requirement was .164% of the diet and 168 mg/day per hen. In Experiment 4, tryptophan supplementation significantly increased egg production at all protein percentages, and the requirement increased as the protein increased. Egg weight was not significantly affected by tryptophan supplementation in any of the four experiments. Hepatic lipid accumulation was generally not decreased by tryptophan supplementation.