This study aimed to evaluate the effect of different reductions in digestible amino acids content (lysine, methionine, and threonine), according to two nutritional requirements in corn, soybean meal, and meat and bone meal based diets, with protease supplementation, on performance parameters and carcass characteristics. A total of 1080 day-old chicks, male, Cobb 500, were allotted to a completely randomized design, in a factorial arrangement 3 x 2, three reductions in digestible amino acids content (lysine, methionine, and threonine) and two nutritional requirements (Rostagno et al. 2005 and Cobb-Vantress Guidelines 2008), and all diets were supplemented with protease (200 ppm) with 6 replicates of 30 birds per pen. There was no significant interaction (p<0.05) between digestible amino acid reductions and both nutritional requirements for the performance variables and carcass yield and cuts. There was an effect of amino acid reduction and protease supplementation only on slaughter weight (p<0.05). Broilers fed according to the nutritional requirements of Rostagno et al. (2005) showed better (p<0.05) performance when compared to broilers fed as specified by the nutritional requirements of Cobb-Vantress (2008) with no significant differences in carcass characteristics. Protease supplementation of corn, soybean meal, and meat and bone meal based diets allows a reduction in the inclusion of crystalline amino acids (lysine, methionine, and threonine).

An experiment was conducted to evaluate broiler chicken performance and carcass yield in response to carbohydrase supplementation (Xylanase and Betaglucanase; XB) and association of carbohydrase and phytase (PHY). A total of 1,920 day-old male broiler chicks (Cobb 500) were distributed in a completely randomized design with 8 treatments and 8 replicates each, allocated in 64 pens with 30 chicks each. The treatments were: Positive Control (PC); Negative Control (NC): reduced ME [-120kcal/kg (Starter) and -170kcal/kg (Finisher)]; NC + XB [50g/ton]; NC + XB [100g/ton]; NC + XB [150g/ton]; NC + XB [50g/ton] + PHY [100g/ton]; NC + XB [100g/ton] + PHY [100g/ton]; NC + XB [150g/ton] + PHY [100g/ton]. The inclusion of XB (150) and XB (50, 100, and 150) associated with phytase increased feed intake than positive control when considering the total rearing phase. The feed conversion ratio of all broilers fed diets with energy reduction were worse than positive control, even with the addition of enzymes, and did not differ between them. There was no significant effect of treatments on carcass parameters.