2 Departamento de Zootecnia/Universidade Federal de Viçosa – UFV. 3 Departamento de Zootecnia/Universidade Federal de Lavras – UFLA.

ABSTRACT- Two experiments were conducted to evaluate the performance, the energy and nutrient balance and economic viability of production of growing pigs fed diets with reduced levels and phytase. In experiment 1, 60 barrows and gilts (initial weight 25 ± 1.72 kg) were housed in a randomized block design with three diets, ten replicates and two animals per experimental unit (one male and one female). One of the diets was formulated with a reduced level with phytase and evaluated in comparison to a positive-control diet that was formulated according to the nutritional recommendations for animals of this breed, and a negative-control diet without phytase. The different diets did not affect feed intake, but the diet with phytase promoted better final weight, daily weight gain and feed conversion, although it did not differ from the positive control diet. In experiment 2, 27 barrows (initial weight 49 ± 3.67 kg) were housed in random blocks with three diets and nine replicates with experimental plot represented by one animal. The diets did not affect the balance of energy and nutrients but had a significant effect on the efficiency of utilization of calcium and phosphorus, which was the lowest in animals that received the positive-control diet. Economic viability improved when nutrients were reduced and phytase was added in the ration. The addition of phytase (500 ftu/kg) in rations formulated with nutritional levels reduced for growing swines improves rearing productivity and it is economical viable