Interrelationship of dietary levels of calcium and phosphorus with phytase and 25-hydroxycholecalciferol in diets for broilers chickens

Two experiments were conducted in wheat and corn based diets. Within each basal diet increasing levels of available phosphorus ranging from 0.35% to 0.50% in increments of 0.05% and 4 different levels of calcium were evaluated, with and without phytase supplementation and with and without Hy-D addition. These combinations resulted in 64 dietary treatments in each experiment that were assigned to six replicates consisting of battery pens with 6 male broilers (Cobb 500). At 18 d body weight and feed conversion were determined. The tibia bones from both legs were taken from all birds to determine incidence of rickets and incidence and severity of tibial dischondroplasia (TD); toes were extracted to determine bone mineralization.;Results of the experiments show that Ca:AP ratios and calcium levels similar or even higher than the recommended by the NRC (1994) are necessary for adequate bird performance. Phytase supplementation improved FCR, whereas the Hy-D addition to diets containing an adequate vitamin D level cause a negative effect on FCR due to an Hypercalcemia condition. Bone development was improved by increasing phosphorus and calcium levels. Consistent reduction of leg abnormalities was obtained by increasing Ca levels. Hy-D addition helped to relief leg problems when suboptimal calcium levels were supplied while the phytase supplementation was effective for this purpose when high Ca levels were given. The use of Hy-D and phytase could be seen as an strategy to alleviate suboptimal Ca:AP ratios.