EFFECTS OF DIETARY CALCIUM, PHOSPHORUS, CA P-RATIO AND PHYTASE ON ZOOTECHNICAL PERFORMANCES AND MINERALIZATION IN BROILER CHICKS/

This trial with 3000 male broiler chicks (0-6 weeks of age) was conduc ted to determine the effect of different dietary combinations of calci um and phosphorus, phase feeding for calcium and/or phosphorus and die tary supplementation of microbial phytase on zootechnical performances and bone mineralisation. The zootechnical performances, feed intake a nd weight gain, were clearly affected by dietary Ca-concentration, but nearly not by phytase supplementation and phase feeding for da and/or P. Feed efficiency was only slightly affected by dietary treatments. Optimal Ca/P-ratio was about 2.2 for maximum weight gain, correspondin g with a Ca- and P-requirement of 0.95 and 0.43% (0-3 weeks of age) an d 0.90 and 0.40% (0-6 weeks ofage), respectively. P-retention can be e nhanced with 50% at equal zootechnical performances. Bone mineralisati on was significantly influenced by dietary treatments. There were diff erences in ash responses between tibia and toe concerning dietary P-co ntent and supplemental phytase. Optimal Ca/P-ratio was about 2.8 for m aximum tibia ash-%, corresponding with a Ca- and P-requirement of 1.04 and 0.36% (0-6 weeks of age). Ca/P-ratio and supplemented phytase inf luence considerably the incidence of tibial dyschondrophasia. Based on linear regression analysis (for tibia ash-%), the average P-equivalen cey value of microbial phytase was 611 units/g P (from mono-calcium ph osphate), thereby varying over a relatively wide range.