Effects of Dietary Levels of Calcium and Nonphytate Phosphorus in Broiler Starter Diets on Live Performance, Bone Development and Growth Plate Conditions in Male Chicks Fed a Wheat Based Diet

A study was conducted to evaluate the effects of dietary levels of calcium, nonphytate P (NPP), phytase and 25-hydroxycholecalciferol (25-OH) on live performance and bone development in male chicks fed a wheat-based diet. Dietary treatments consisted of a 2 x 2 x 4 x 4 factorial arrangements with two levels of supplemental phytase (0 or 1200 FTU/kg), two levels of 25-OH (0 or 69 μg/kg), four levels of calcium (0.20% less than a 2:1 ratio of Ca to NPP; 2:1 ratio of Ca to NPP; 0.20% Ca greater than a 2:1 ratio of Ca to NPP; 0.40% Ca greater than a 2:1 ratio of Ca to NPP) and four levels of NPP (0.35, 0.40, 0.45 and 0.50%) for a total of 64 treatments. The primary basal diet used to mix all experimental diets was supplemented with a complete vitamin mix containing 5500 IU of cholecalciferol. Each diet was fed to two pens of six male chicks of a commercial broiler strain in electrically heated battery brooders for three consecutive trials using the same diet mix for a total of six replicates per treatment. At 18 d birds were weighed, feed consumption determined and all birds killed for bone measurements. Toes from all birds within a pen were removed and ashed. Tibiae from both legs were removed and scored for incidence and severity of tibial dyschondroplasia and for incidence of calcium or phosphorus rickets. Ca: NPP ratios and calcium levels similar or higher than NRC (1994) recommendations appear necessary for adequate bird performance. Phytase supplementation improved performance parameters such as FCR and body weight, whereas the addition of 25-OH to diets already containing 5500 IU/kg of cholecalciferol had a negative effect on FCR due to a possible hypercalcemia condition. Bone development was improved by increasing phosphorus and calcium levels. Moreover, supplementation with 25-OH and its combination with phytase were effective in enhancing bone development. Increasing Ca levels consistently reduced leg abnormalities. Addition of 25-OH helped to relieve leg problems when suboptimal calcium levels were supplied while phytase supplementation was effective for this purpose when high Ca levels were given. The addition of these additives could be seen as an strategy to alleviate problems with suboptimal Ca: NPP ratios.