Phytase superdosing in broiler diets containing animal-derived protein: effects on performance, bone mineralisation...

1. This study evaluated the effects of phytase superdosing in broiler chicken diets based on corn, soybean meal and meat and bone meal on performance, carcass yield, pectoral myopathies, bone mineral composition and the metabolisability of energy and nutrients.2. Two experiments were conducted: one focused on performance and the other on nutrient metabolism. In both experiments, birds were randomly assigned to a completely randomised experimental design. The performance trial included 1600 male Cobb 500 broilers, whereas the metabolism trial included 480 birds of the same strain. In the performance trial, birds were allocated to one of eight treatments with 10 replicates of 20 birds per experimental unit from 1 to 42 d of age. In the metabolism trial, each experimental unit consisted of six birds. Linear and quadratic regression analyses were performed to estimate the optimal phytase supplementation level.3. Higher phytase inclusion levels, particularly 2000 phytase units/kg feed, resulted in greater weight gain and better feed conversion ratio. Diets supplemented with 2000 and 2500 phytase units/kg caused the highest calcium and phosphorus concentrations in tibia bones.4. In the nutrient metabolisability trial, phytase supplementation promoted linear increases in metabolisability coefficients for gross energy, organic matter and zinc, along with linear reductions in excreted mineral matter and zinc.5. Overall, phytase superdosing, especially at 2000 and 2500 phytase units/kg, enhanced broiler performance, increased bone mineral deposition, improved nutrient metabolisability by 7 to 29% and reduced phosphorus excretion by up to 31.6%.6. These findings demonstrated that high-dose phytase can be an effective strategy to improve feed efficiency and nutrient utilisation in broiler diets containing mixed phosphorus sources, including animal-derived ingredients.