Efficiency of microbial phytase supplementation in dietsformulated with different calcium:phosphorus ratios, supplied tobroilers from 22 to 33 days old

Abstract

An experiment was conducted with broilers from 22 to 33 days of age to evaluate the efficiency of six microbialphytases supplemented in diets (1500 FTU/kg) that were formulated with three different calcium:available phos-phorus (Ca:Pavail) ratios (4.5:1.0, 6.0:1.0 and 7.5:1.0). A positive control diet without phytase was formulatedwith a Ca:Pavailratio of 7.5:3.4 to meet the nutritional requirements of the broilers. The P and ash contents of thetibia, magnesium in the plasma, performance, balance and retention of phytate phosphorus (Pphyt), intake oftotal P and nitrogen (N), nitrogen-corrected apparent metabolizable energy and apparent digestibility of dry mat-ter of the diets were not influenced (p > 0.05) by the type of phytase or the dietary Ca:Pavailratio. However, therewas an interaction (p < 0.05) between the phytase type and the Ca:Pavailratio for the retention coefficients oftotal P, Ca and N. Phytase B resulted in the highest Ca deposition in the tibia (p < 0.01). Phytases D, E and Freduced the Ca concentrations in the tibia (p < 0.01) and plasma (p < 0.05). Phytase D increased the P level inthe plasma and decreased the total P excretion (p < 0.01). Phytases E and F increased Ca excretion, while phy-tase A reduced it (p < 0.01). Regardless of the phytase type, increasing the dietary Ca:Pavailratio reduced(p < 0.05) the plasma P concentration and the excretion of total P and N and, conversely, increased (p < 0.05)the plasma concentration, intake and excretion of Ca. For the rearing period evaluated, it is possible to reducethe Pavailof the diet to 1.0 g/kg when Ca is maintained at 7.5 g/kg, and the diet is supplemented with 1500 FTUof phytase A, C, D or E/kg. This diet allows the maintenance of performance and adequate bone mineralization,and it improves the Ca, total P and Pphytutilization in addition to reducing the excretion of N and P into theenvironment.