The addition of protease to broiler diets may complement the action of endogenous enzymes and improve protein digestibility. Here, the authors evaluated the effect of adding protease to broiler diets that contained animal-based meal on bird performance, digestibility, and biometry of digestive tract organs. Four treatments, which contained animal- or plant-based meals with or without supplementary protease were compared, namely basal vegetable feed (BVF), BVF + protease (BFP), basal vegetable

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... ed + animal by-product meal (BFA), and BFA + protease. In the first experiment, 320 one-day-old Cobb 500® chicks were allocated to eight replicates with 10 birds per replicate. The experimental period was seven days, and nutrient metabolizability was evaluated. In the second experiment, 720 one-day-old Cobb 500® chicks were assigned to treatments in a similar manner, with six replicates and 30 birds per replicate, but the experimental period was 42 days. Significant differences (P <0.05) were observed between treatments for nutrient digestibility, weight gain, feed consumption, average final weight, food conversion, viability, and biometry of the pancreas. Treatments with animal-based meals had the highest digestibility. Birds fed these meals grew faster in the pre-starter phase and consumed less feed between 1 and 21 days. However, between 1 and 42 days old, broilers fed plant-based diets had better feed conversion, and the group that did not receive protease supplementation had a better liveability rate.Keywords: additive, exogenous enzyme, nutrition, organ biometry, poultry