Effects of dietary calcium and phosphorus levels on broiler production and blood biochemistry in phytase-supplemented diets

Numerous publications have reported the detrimental effects of calcium (Ca) over-feeding on broiler performance and nutrient digestibility, but its impact on blood biochemistry related to nutrient metabolism is not clear. The current study aimed to evaluate the effects of Ca and phosphorus (P) on broiler production and blood metabolites in phytase-supplemented diets. A 3 × 2 factorial arrangement was applied, including 3 Ca levels (Low, Medium or High) and 2 non-phytate P (nPP) levels (Marginal or Adequate). The experimental diets were corn-SBM based, and a phytase product (HiPhorius^TM, dsm-firmenich, Switzerland) at 1000 FYT/kg was supplied in all the diets. There were 40 birds/pen and 8 pens/treatment. The results showed significant interactions between Ca and P levels (P < 0.05) during the starter phase: High Ca increased (P < 0.05) feed conversion ratio (FCR) and plasma uric acid compared to Low Ca with Marginal nPP level, while High Ca improved (P < 0.05) tibia ash compared to Low Ca with Adequate nPP level. However, these interactions diminished as birds aged, only significant main effects of Ca level (P < 0.05) were observed on these parameters in the finisher phase. Compared to Low Ca, High Ca showed lower (P < 0.05) body weight (BW) gain and higher (P < 0.05) BW-corrected FCR at 0-42 d of age, higher (P < 0.05) tibia ash and breaking strength, and higher (P < 0.05) plasma uric acid at 43 or 44 d of age. The increase of plasma uric acid with High Ca may indicate a possible competition in the renal system to regulate nitrogen metabolism and Ca/P homeostasis, presumably compromising protein accretion. Additionally, High Ca showed significantly higher (P < 0.05) footpad lesion scores compared to Low Ca, especially with Marginal nPP level. In conclusion, a decrease of dietary Ca may improve growth performance and footpad lesion scores by alleviating renal burden through its hypocalciuretic effect, but this comes at the expense of reduced bone mineralization and breaking strength. Therefore, the dietary Ca level is recommended to be adjusted according to specific production objectives in broiler operations.