Present study was conducted to establish Tryptophan (Trp) needs of Xinyang green-shell laying hens by evaluating its effect on laying performance, egg quality, antioxidant capacity, and the immune functions. A total of 525 laying hens, 28 weeks of age, were randomly allocated to five treatment groups, each of which included 5 replicates of 21 hens. Hens were fed the basal diet based on corn and soybean meal for 12 weeks. L-Trp was added to the control diet at 0.0 0.02, 0.04, 0.06, and 0.08%, respectively, to achieve 0.15, 0.17, 0.19, 0.21 or 0.23% Trp. Laying rate, average egg weight, and feed conversion ratio (FCR) were significantly increased by Trp levels from 0.19 to 0.23%. Dietary Trp from 0.17 to 0.19% increased egg internal quality (albumen height and haugh unit) rather than external quality. Supplementing with Trp increased glutathione peroxidase and total superoxide dismutase activity, total antioxidative capacity concentration and decreased malondialdehyde concentration. Serum IgA concentration increased at 0.21–0.23% dietary Trp, while serum IgM increased linearly in response to dietary Trp levels. We suggest that the optimum level of dietary Trp was ranged from 0.19 to 0.21% for Xinyang green-shell laying hens under the current study conditions.
Part of the book: Amino Acid