Performance and bone quality of broilers fed diets containing different levels of phosphorus and supplemented with phytase

Background: Although phytase has been widely used in poultry nutrition, the effects of the enzyme on broilers fed low levels of phosphorus are poorly understood. Objective: To evaluate the effects of two commercial phytases on live performance and bone quality of broilers fed diets with normal and reduced levels of phosphorus. Methods: Two experiments were conducted with four treatments and six repetitions with 30 birds each, for a total of 24 groups. The first experiment (Exp. I) used a reference level of available phosphorus (AP) with four treatments, as follows: Positive control= 0.45% AP starter diet/0.40% AP grower diet without phytase; Phytase X= 0.35% AP starter diet/0.30% AP grower diet + Phytase X; Phytase Y= 0.35% AP starter diet/0.30% AP grower diet + Phytase Y; and Negative control= 0.35% AP starter diet/0.30% AP grower diet, without phytase. In experiment II (Exp. II) the same treatments were used, but AP levels were reduced by 0.10%. The variables analyzed were: performance from one to 35 days, and bone quality at 35 days of age. Both experiments were analyzed using a completely randomized design. Results: In Exp. I, the positive control resulted in greater body weight gain (2,558 g; p<0,05) compared to Phytase Y (2,470 g) and negative control (2,472 g), and better feed conversion ratio (1.48; p<0,05) than the negative control (1.51). However, when phosphorus was reduced in Exp. II, the positive control and treatments with Phytase X showed better results (p<0.01) for feed intake (3,608 g and 3,593 g, respectively) and weight gain (2,430 g and 2,400 g, respectively) compared to the negative control (2,889 g of feed intake and 1,915 g of weight gain; p<0.01), which also presented low bone ash (36.8%) and phosphorus in the tibia (5.48%; p<0.01). Conclusion: Reducing AP concentration in diets not added with phytase negatively affects weight gain and feed intake of broilers.