Niveis crescentes de protease em dietas para frangos

Abstract

Three experiments were conducted to evaluate the optimal level of protease enzyme supplementation for broiler chickens based on performance parameters, carcass yield, and amino acid (AA) digestibility. In the first experiment, performance and carcass yield of broilers supplemented with different levels of protease enzyme in diets with reduced indigestible AA fraction, based on corn and soybean meal, were evaluated from 1 to 42 days of age. Ten diets were used in a feeding program format according to the growth phase. A basal diet and diets with reduced indigestible AA fraction were supplemented or not with three protease inclusion levels: 4,000 UP/kg, 8,000 UP/kg, and 12,000 UP/kg. The inclusion was analyzed in two periods: 1-21 days and 22-42 days of age to evaluate the effect of protease inclusion in each phase and its accumulated effect over the entire 1-42 days period. For performance variables, broilers fed the pre-initial phase with 12,000 UP/kg in diets with reduced indigestible AA fraction showed increased weight gain, similar to those fed the basal diet. In the 1-42 days period, a quadratic effect on feed conversion was observed, with the best conversion at 6,243 UP/kg of protease. Regarding carcass and cut yields, no statistical differences were observed between treatments. It was concluded that protease supplementation in diets with reduced nutritional levels improved broiler performance. The other two experiments aimed to evaluate the effect of different protease levels on ileal amino acid digestibility. The first experiment (1) assessed the apparent ileal digestibility coefficients (AIDC) of amino acids in the diet, and the second experiment (2) assessed the apparent and standardized ileal digestibility coefficients (SIDC) of amino acids in the ingredients, corn and soybean meal, for broilers in the early phase. In experiment 1, treatments consisted of: basal diet; reduced indigestible AA fraction diet (RR); RR + 8,000 UP/kg; and RR + 12,000 UP/kg. A completely randomized design (CRD) with four treatments and six replicates of 10 birds each was used. The RR + 8,000 UP/kg treatment significantly improved the AIDC of AA in the diet. In experiment 2, treatments consisted of a protein-free diet (RIP) containing corn or soybean meal, supplemented or not with two levels of protease enzyme (8,000 UP/kg or 12,000 UP/kg). A completely randomized design (CRD) with seven treatments and six replicates of 15 birds each was used. The 8,000 UP/kg level increased the SIDC of AA in soybean meal, and the 12,000 UP/kg level significantly increased the SIDC of AA in corn. The addition of protease to broiler diets in the early phase is effective in increasing the digestibility coefficients of amino acids in the diet, corn, and soybean meal. It is recommended to use 12,000 UP/kg of protease in broiler diets, as this level improved weight gain without compromising bird viability.