Efficiency of microbial phytases in diets formulated with different calcium:phosphorus ratios supplied to broilers from 35 to 42 days of age

摘要

ABSTRACT The aim of this study was to investigate the efficiency of six microbial phytases (named of A to F) supplemented in diets (1500?￠????FTU/kg) formulated with three different calcium:available phosphorus ratios (3.5:1.0, 5.0:1.0 and 6.5:1.0). Moreover, one positive control diet without phytase that was formulated with a calcium:available phosphorus (Ca:AP) ratio of 6.5:3.0 was also considered. The utilization of dietary nutrients, as well as the bone, plasma and performance parameters of broilers from 35 to 42 days of age was evaluated. Phytase D increased the P and magnesium plasma concentrations. Broilers fed diets containing phytase B showed a lower feed intake and weight gain, while the birds fed diets containing phytase E consumed more feed, gained more weight and excreted less total P. The highest Ca retention and also the best nitrogen utilization were determined when the diet contained phytase D or E. For all phytases evaluated, an increased in the dietary Ca:AP ratio increased the tibia ash content and the Ca balance. Phytase utilization reduced the phytate P excretion, improving its utilization by the broilers. For the rearing period evaluated, it is possible to reduce the AP of the diet to 1.0?￠????g/kg when Ca is maintained at 6.5?￠????g/kg, and the diet is supplemented with 1500?￠????FTU of phytase A, B, C, D or E/kg. This diet allows the maintenance of performance, optimizes the bone mineralization, and it improves the Ca, total P, phytate P and nitrogen utilization in addition to reducing the P excretion.