Evaluation of an indigenous source of rock phosphate as a supplement for broiler chickens

This study investigated the effects of replacing dicalcium phosphate (DCP) with Hazara rock phosphate (HRP) on the growth performance of broiler chickens. The purpose was to determine the maximum level of F that could be well tolerated. The HRP (13.16% P and 2.98% F) was incorporated into a standard corn- and soybean meal-based diet by replacing 0, 25, 50, 75, and 100% of DCP based on P. Each treatment consisted of 5 replicate pens of 10 chicks each. The Ca and nonphytate P contents of all diets were maintained constant at 1.0 and 0.45%, respectively. Replacing 25% DCP with HRP significantly increased average BW gain. Substituting 100% HRP (562 mg of F/kg) decreased (P < 0.05) BW gain. The BW gain was maximized at 63.5:36.5 (DCP:HRP) using a quadratic relationship: BW gain (g) = 1,128.6 + 2.6848 × HRP - 0.0368 × HRP(2). Increasing the level of HRP decreased feed intake: feed intake (g) = 1,987.4 + 2.775 × HRP - 0.0515 × HRP(2). The effect of HRP was not pronounced (significant at P < 0.05) until 75% of DCP was replaced by HRP. Feed intake decreased by an average 3.77 g with each 1.0% increase in the levels of HRP beyond 27% HRP substitution. Replacing DCP with HRP up to 50% caused a significant increase in hot carcass weights. The Ca content of tibia was a quadratic function of HRP and was predicted to be highest at 56% HRP substitution. However, increasing HRP in the diet gradually decreased tibia P content (linear function). Serum Ca was increased by substituting HRP for DCP (linear effect). Increasing HRP in the diet decreased the P content of the serum and was predicted to be lowest (P < 0.05) beyond 50% HRP substitution, suggesting poor P availability at high HRP. In conclusion, growth was maximized by feeding about 36.5% HRP (205 mg of F/kg) and 63.5% DCP as P supplements. Using a multiple range test, it was concluded that between 25 and 50% DCP with HRP replacement (141 and 281 mg of F/kg, respectively) could be used safely without significantly decreasing the growth performance of broiler chickens.