Starter Diets on Live Performance, Bone Development and Growth Plate Conditions in Male Chicks Fed a Wheat Based Diet1

Abstract: 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 diet