Effects of Dietary Crude Protein and Protease Levels on Performance, Immunity Capacity, and AA Digestibility of Broilers

Exogenous proteases are promising to stimulate the application of low-protein diets for broilers. A total of 540 1-day-old Arbor Acres male broilers were randomly assigned to 9 groups with 6 replicates of 10 birds. A 3 × 3 factorial, completely randomized arrangement was used to evaluate the effects of dietary crude protein (CP) and protease levels on growth and slaughter performance, immunity capacity, and apparent ileal digestibility (AID) of amino acids (AA). Dietary CP levels were 20.0%, 19.5%, or 19.0% during the starter phase, and 18.0%, 17.5%, or 17.0% during the finisher phase. Protease levels were 0, 250, or 500 mg/kg in diets throughout the trial. The trial lasted for 42 days. Weight gain and feed efficiency of broilers decreased as dietary CP lowered, but improved with protease supplementation. Dietary CP and protease levels had few effects and interactions on carcass characteristics, immune organ indexes, and immunoglobulin concentrations. The AID of most AA was improved by dietary CP decrease or protease supplementation. In conclusion, reducing dietary CP decreased the performance and immune capacity of broilers but increased the AID of AA. Almost independent of dietary CP level, dietary protease addition improved the performance of broilers, probably through the enhancement of AA digestibility, and had no effect on carcass traits.