effect of using nutrient equivalency of phytase on broiler chicks’ performance

an experiment was conducted using 640 day-old sexed commercial broiler chicks (ross 308 strain) from 10 to 49 days of age. the experimental design was a completely randomized factorial one. the experimental units (pens) contained 20 chicks each and were allotted at random to 4 dietary treatments × two sexes with 4 replicates per treatment. four dietary treatments were formulated based on corn and soybean meal in mash form. all the diets were iso-protein and iso-energetic. the first dietary treatment was formulated without phytase, the second one containing 500 ftu/kg natuphos phytase, and the third 500 ftu/kg natuphos phytase (calculated equal to half of the nutrient equivalency values for natuphos phyatse). the forth dietary treatment contained 500 ftu/kg natuphos phyatse (calculated as the total nutrient equivalency values for phytase). body weight gain, feed intake, and conversion ratio were assessed for grower (10-29 d), finisher (29-49 d), and the whole rearing period (10-49 d), separately. also, carcass measurements, toe ash percentage, calcium and phosphorus concentration in toe ash, and blood phosphorus concentrations were evaluated at the end of the experiment. the results indicated that addition of phytase to diet significantly increased toe ash, and toe ash calcium as well as phosphorus content in male and female broiler chicks. the effect of sex was significant on body weight gain, feed intake, feed conversion ratio in grower, and in finisher period, toe ash percentage, ca and p concentration as well as production number. interaction between sex and dietary treatment was significant in terms of grower body weight gain, grower feed intake, as well as phosphorus content of toe ash. in summary, microbial phytase enhanced growth performance, and the calculation of nutrient equivalency values of phytase led to uniform performance in all dietary treatments, and as well as the reduction of production costs.