The dynamic requirements of tryptophan in the broilers at different growing stages under low-protein diets

The experiment was conducted to clarify the dynamic requirement of tryptophan (Trp) in broilers under low-protein diets and construct a prediction model based on the Trp requirement. A total of 1080 male and 1080 female Arbor Acres broilers at 0 d old were randomly assigned to 6 treatments and allotted to 3 stages: 0 to 14 d starter, 15 to 28 d grower, and 29 to 42 d finisher. The birds in the control group (group NC) were fed with conventional protein diets with nutrient levels formulated to breeder recommendations. The experimental groups (groups Ⅰ to Ⅴ) were fed low-protein diets with different Trp levels which were 80% (group Ⅰ), 90% (group Ⅱ), 100% (group Ⅲ), 110% (group Ⅳ) and 120% (group Ⅴ) of NC group, respectively. The results showed that the optimal response dose of Dig.Trp/Dig.Lys was 0.172 to 0.175 for female broilers, 0.163 to 0.170 for male broilers in starter stage; 0.167 to 0.175 for female broilers, 0.168 to 0.176 for male broilers in grower stage; 0.175 to 0.177 for female broilers in finisher stage. The dynamic model of Dig.Trp/Dig.Lys daily requirement on average metabolic BW and ADG was y = 0.835 × BW^0.75-1.745 × ADG-24.181 for females and y = -0.054 × BW^0.75 + 0.434 × ADG-0.107 for males in starter phase; y = -0.208 × BW^0.75 + 0.759 × ADG + 12.686 for females and y = -0.028 × BW^0.75 + 0.523 × ADG-11.082 for males in grower phase; y = 0.393 × BW^0.75-0.286 × ADG-91.961 for females and y = 0.146 × BW^0.75 + 0.323 × ADG-55.300 for males in finisher phase. The optimal response Trp level in low-protein diets for growth performance can also positively regulate the development of immune organs, serum ALT, AST, immunoglobulins and hormone levels. In conclusion, optimal dietary Trp supplementation in broilers fed low-protein diets resulted in increased growth performance along with improved immune system and stress status. This research provides precise nutritional strategies to enhance poultry performance and efficiency.