Performance and bone integrity of broilers receiving dietary calcium at lower concentrations than current recommendations

Abstract

alcium and phosphorus are the two major macro-minerals required for proper growth and bone mineralisation in broiler chickens. Typical feed ingredients in broiler rations are low in calcium and phosphorus and inorganic sources of calcium and phosphorus are therefore used to supplement the shortfall. The phosphorus present in the feed ingredients is mostly in phytate form which is unavailable to the chicken. The hydrolysis of phytate with exogenous phytase helps to decrease the required amount of inorganic calcium and phosphorus in the diet, reduce the environmental effect of broiler production and reduces costs. However, calcium and phytate-phosphorus are known to form complexes that are resistant to the hydrolytic effect of phytase and are indigestible. Thus, excess calcium will reduce the amount of phosphorus available to the broiler chicken thereby impairing broiler performance. The main objective of this study was to determine if calcium inclusion levels lower than currently recommended by Aviagen for Ross broilers, will enhance broiler production without impairing bone mineralisation. Current Ca:P recommendations from Aviagen is 2:1. In order to achieve the objective, Ross 308 day-old chicks were randomly assigned to eight different treatments varying in calcium and phosphorus inclusion levels. The trail was designed to evaluate the interaction between dietary calcium and non-phytate phosphorus. Broiler performance, bone ash percentage and bone breaking strength were the parameters used to evaluate the interaction. In this trial, 64 pens were used to allow for eight replications for each of the eight treatments. Sixty unsexed chicks were placed in each pen. The Ca inclusion levels ranged from 0.70% to 0.95% and was tested with three different P inclusion levels. The Ca:P ratio ranged from 1.54:1 to 2.50:1. The treatments were fed through a starter, grower and finisher phase and no phytase was included in the diet. Thirty two chicks per treatment were euthanised on 14, 32 and 35 days of age when the tibias were removed for analysis of bone ash and bone breaking strength. From the performance data obtained from this trial, it was clear that an interaction between calcium and phosphorus existed. The treatment diet with a Ca:P ratio of 1.60:1 resulted in the highest body weight and lowest feed conversion ratio of broilers at 35 days of age. As the Ca:P ratio increased, the body weight and feed intake decreased. The bone ash percentage was linked to the amount of calcium and phosphorus in the diet. As the mineral content of the diet increased the bone ash percentage of broilers at 14 and 35 days of age also showed an increase. The bone breaking strength increased as the calcium concentration in the diet increased. It can be concluded that reducing the amount of calcium in the diet below the current Aviagen recommendation for Ross broilers improves broiler performance without compromising bone mineralisation.