Phytic acid is an anti-nutritional constituent of plant derived feeds. As a reactive anion, it forms a wide variety of insoluble salts with minerals including phosphorus, calcium, zinc, magnesium and copper. Phytic acid is also known to form complexes with protein and proteolytic enzymes (pepsin and trypsin). Because of the lack of endogenous phytase enzymes that hydrolyze phytic acid; phosphorus, calcium, protein and other phytic acid bound nutrients are less available to poultry. Commercially-available microbial phytase has great nutritional significance and ecological importance. Poultry diets supplemented with microbial phytase result in improved growth performance and increased digestibility and availability of phytate bound phosphorous, calcium, zinc and copper. Microbial phytase supplementation has also been shown to increase ileal digestibility of crude protein and amino acids. The efficacy of supplemental microbial phytase depends on its rate of inclusion, dietary calcium and phosphorus ratio, vitamin D 3 , nature of diet, age and genotype of birds. Thus, microbial phytase can be used to exploit the inherent nutritional potential of feedstuffs for more economic and environmentallyfriendly poultry production.

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An experiment was conducted to evaluate the effects of phytase supplementation on the growth performance, nutrients utilization and bone mineralization in broiler chickens. Day-old broiler chicks (n=480) were equally devided into eight treatment groups and fed maize or wheat based isocaloric, isonitrogenous and isocalcium diets having two non phytate phosphorus (NPP) concentrations (0.50% and 0.30%) and two phytase levels (0 and 500 phytase units/kg diet) in a 42 days growth trial. Maize based dietary treatments were MC (NPP 0.50%, MN (NPP 0.30%), MNP (MN+500 units of phytase) and MCP (MC+500 units of phytase), whereas wheat based experimental diets were WC (NPP 0.50%), WN (NPP 0.30%), WNP (WN+500 units of phytase) and WCP (WC+500 units of phytase). The NPP levels were maintained by dicalcium phosphate. Reduction in dietary NPP depressed live weight gain and feed intake and increased feed conversion ratio (FCR). Phytase supplementation to low NPP (0.30%) diets significantly (p<0.05) improved the growth performances of broilers. The supplementation to low NPP diets allowed complete, safe and economic replacement of dietary inorganic P (dicalcium phosphate) to reduce feed cost per kg live weight gain of broilers. Reduction in dietary NPP did not affect retention of nutrients except phosphorus (P) but had a significant (p<0.05) depression in tibia ash and minerals (Ca, P) concentration in serum and tibia ash. Phytase supplementation at low NPP level was effective (p<0.05) in improving the retention of dry matter, Ca and P and Ca and P concentration in serum and tibia ash. However, the supplementation was not effective at high level of NPP (0.50%). There were no significant (p>0.05) differences in carcass quality among dietary treatments. The response of phytase was greater in low NPP and maize based diets as compared with high NPP and wheat based diets, respectively. The results show that phytase supplementation to low NPP (0.30%) diets improved the growth performance, relative retention of nutrients (N, Ca and P) and minerals (Ca, P) status of blood and bone in broiler chickens, with a better efficacy in maize based diets.