Relationship of calcium, phosphorus and phytase to broiler growth performance from day 1 to 21

It has been shown that an ileal digestible phosphorus (IDP) value of 2.0 g/kg can support optimum bird performance (Li et al., 2017). However, the relationship of this value to dietary Ca concentration and phytase supplementation is still unclear. The aim of this study was to further clarify these interrelationships.

Four hundred, day old, Ross, male broiler chicks were fed experimental diets based on wheat, sorghum, canola meal, soybean meal and meat and bone meal. The diets contained 1 level of IDP (2.0 g/kg) and 4 concentrations of Ca (3.5, 4.0, 4.5 & 5.0 g/kg) either with or without phytase (Axtra PHY 10000 TPT, 500 FTU/kg diet, Feedworks, Australia) supplementation. Each experimental diet was fed to 5 replicate pens with 10 birds per replicate: starter diet from days 1 to 14 and the grower diet from days 15 to 21 post-hatch. All birds had free access to feed and water. Body weight and feed intake were recorded weekly and the feed conversion ratio (FCR) was calculated.

The results (Table 1) indicate that the dietary Ca concentration had a significant effect on chick performance. Without phytase supplementation, feed intake and body weights were lower as the Ca to P ratio increased (P < 0.05). However, with phytase supplementation the detrimental effect of a high Ca to P ratio was alleviated. The results indicate that phytase reduced the negative impact of Ca on body weight (P=0.025) and feed intake (P=0.02). Similar numerical differences were seen with FCR. These results highlight the importance of delineating the bioavailability of both Ca and P in relation to phytase supplementation of current broiler diets.

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