Dietary concentrations of phosphorus and calcium and broiler performance throughout the growing cycle

Phosphorus (P) is a non-renewable resource and will become increasingly scarce during this century. Nevertheless, excessive usage of P in the poultry industry results in additional costs and also increased P excretion, causing eutrophication and land erosion. Tackling these problems requires better understanding of P bioavailability and the P requirements of the bird. Furthermore, the evolution of phytase technology has necessitated a reevaluation of P and calcium (Ca) requirements for poultry. An important consideration when studying P is dietary Ca concentration and, in this study, different dietary concentrations of both minerals were evaluated throughout the 49 day broiler growth cycle.

Four hundred, day old, Ross 308, male broiler chicks were fed experimental diets based on a sorghum-wheat blend and soybean meal to which were added xylanase (Axtra XB 201 TPT, 100g/metric tonne, Feedworks, Australia) and phytase (Axtra PHY 10000 TPT, 500 FTU/kg diet, Feedworks, Australia). The diets contained combinations of Ca and P that had been shown in our previous experiments (Li et al. 2017) to support optimum broiler performance. Ileal digestible P (IDP) concentrations of 2.0 and 2.5 g/kg were each combined with two Ca concentrations (4.5 and 6.5 g/kg). The highest concentration of IDP fed was 3.0 g/kg in combination with Ca of 3.5, 4.5, 5.5 or 6.5 g/kg. The same concentrations of both minerals were maintained in the starter, grower and finisher diets. Each experimental diet was fed to 5 replicates with 10 birds/replicate. No statistical differences (P> 0.05) were found in final body weight (4554g), feed intake (140 g/bird/day) or feed conversion ratio (1.52) between the 8 treatments, indicating that an IDP value of 2.0g/kg combined with 4.5g/kg Ca would support optimum broiler performance. In a subsequent study (Cheng et al. 2017), lower concentrations supported optimum performance from day 1-21 post-hatch.

ACKNOWLEDGEMENT: Research was funded by the RIRDC Chicken Meat Program.