ADIÇÃO DE FITASE EM RAÇÕES COM DIFERENTES NÍVEIS DE ENERGIA METABOLIZÁVEL, PROTEÍNA BRUTA E FÓSFORO DISPONÍVEL PARA FRANGOS DE CORTE DE 1 A 21 DIAS

The objective of this study was to evaluate the performance and the pollutant excretion of broilers from 1 to 21 days of age fed diets with different levels of metabolizable energy (MEn), crude protein (CP) and available phosphorus (aP), supplemented with amino acids and phytase. To evaluate the performance, 1,350 Cobb broilers at one day of age (weight of 45.5 ± 0.9g) were distributed in a completely randomized design in a 4x2+1 factorial arrangement (four levels of MEn – 2,850; 2,950; 3,050 and 3,150 kcal/kg – and two of CP and aP – 17 with 0.34% and 19 with 0.25%, respectively, all with phytase, and an additional treatment – control, without phytase, with 21% PB, 3,000 kcal/kg MEn and 0.46% aP), in six replications with 25 birds. To evaluate the excretion of pollutants, 270 broilers at 14 days of age were allotted in metabolic cages in groups of five during seven days, using the same statistical design. Although the use of phytase reduced phosphorus and copper excretion, it decreased weight gain and increased feed conversion ratio in all studied nutritional plans. In phytase-diets, the energetic levels linearly reduced feed intake and improved feed conversion ratio and calcium and potassium excretion. Energy reduced the nitrogen, phosphorus and zinc excretion only in 17% CP and 0.34% aP diets. Crude protein reduction in phytase-diets improved feed conversion ratio and reduced nitrogen and potassium excretion. It was concluded that phytase decreases broiler performance until the third week of age when combined with reduced levels of CP and aP in diets. KEYWORDS: additive; enzyme; excrement quality; ideal protein; nutrition.