COMPARATIVE EFFECTS OF MICROBIAL PHYTASE AND INORGANIC PHOSPHORUS ON PERFORMANCE AND ON RETENTIONS OF PHOSPHORUS, CALCIUM AND CRUDE ASH IN BROILERS

A two-factorial experiment was carried out with male day-old broiler chickens for two weeks to compare the effects of graded supplements of microbial phytase, inorganic phosphorus (P) and a combination of Ca and P (Ca + P) on performance, on whole-body retentions of P, Ca and crude ash and on toe-ash. A corn-soybean meal ration containing (per kg) 2.3 g phytate-P, 1 g P from MCP, 4.5 g total P and 6 g Ca was used. Each treatment was fed to four replicates of 12 chickens kept in batteries under 24 h lighting. Liveweight gain was improved by phytase, P and P + Ca (p less-than-or-equal-to 0.05), but not by Ca. The differences in liveweight gain were largely due to differences in feed intake, while feed conversion was not significantly affected. The retentions of Ca, P and crude ash were improved significantly (p less-than-or-equal-to 0.05) by phytase, P and P + Ca, but not by Ca. P-retention was linearly related to supplemental phytase (r2 = 0.75) and P (r2 = 0.82), respectively. From the regression equations 700 U phytase were calculated to be equivalent to 1.0 g P. The highest phytase level studied (800 U/kg) resulted in a retention of total P of 67 % of intake compared with 53 % in the control group. Toe-ash weight was linearly related to P-retention (r2 = 0.76). This indicates that toe-ash, which has been used as an indicator of P-retention in turkey poults, is also useful in 2-week-old broilers.