The objective of this trial was to determine the adequate level of the phytase (0, 300, 600 and 900 PU/kg of the diet) to be added in corn-soybean meal diets with two crude protein (CP) levels, one at the animal requirements (18%CP) and another at smaller level (16% CP), for the most effective nitrogen bioavailability, of the energy and of the macro minerals, and also to observe in which of these diet protein levels the phytase has larger effect. Twenty-four pigs with initial weight of 18,4 kg were housed in metabolic cages for metabolism assay of the nitrogen, gross energy, phosphorus and calcium, through the method using ferric oxide as a marker. The diets were supplied in accordance to the animal's metabolic weight, and they were isoenergetic with 3295 kcal of ME/kg. The animal performance traits, the nitrogen digestibility (ND), nitrogen retention (NR), digestive energy (DE), metabolizable energy (ME), phosphorus digestibility (PD), phosphorus retention (PR), calcium digestibility (CaD) and calcium retention (CaR) were evaluated. An increase in the nutrient bioavailabilities were observed to the added phytase in the levels from 220 - 508 UF/kg of the diet, except in the animal's performances that increased linearly. When energy was evaluated, the enzyme efficiency was better when it was added in marginal protein diet levels, 16% CP, as compared with diets of 18% CP.
digestibility; energy; enzyme; metabolism; phytate
