Effect of Protease Supplementation in Diets with or Without Copper Sulfate and Formaldehyde on the Standardized Digestibility of Amino Acids in Broiler Chickens

With the growing demand for sustainable and cost-effective poultry production, optimizing nutrient utilization is crucial. Exogenous proteases enhance protein digestibility, reduce nitrogen excretion, and improve feed efficiency, but their interaction with additives like copper sulfate (CuSO₄) and formaldehyde remains unclear. This study evaluated the combined effects of protease with these additives on amino acid digestibility, performance, and bone quality in broilers. A total of 500 broilers were assigned to seven dietary treatments, each replicated 10 times (six birds per cage) over 21 days (14 days of adaptation and 7 days of evaluation). Treatments included a reference diet (RD), RD + CuSO₄ (600 g/ton, 150 mg Cu/kg), RD + formaldehyde (2000 g/ton), with or without protease supplementation (30,000 NFP/kg), and a protein-free diet. Protease improved protein digestibility (2.50%) and amino acid digestibility (essential: 2.64%; non-essential: 2.52%) in diets with CuSO₄ or formaldehyde (<i>p</i> < 0.05). CuSO₄ alone had no effect, but its combination with protease significantly enhanced crude protein digestibility (4.63%). Formaldehyde reduced amino acid digestibility, but protease mitigated this negative effect (-4.68% vs. -1.81%). Protease also improved feed conversion and bone strength. These findings demonstrate that protease combined with CuSO₄ or formaldehyde optimizes nutrient digestibility, enhances broiler performance, and supports sustainable poultry production.