Effect of dietary calcium level and source on mineral utilisation by piglets fed diets containing exogenous phytase

Abstract

Calcium and phosphorus are essential minerals, closely linked in digestive processes and metabolism. With widespread use of low P diets containing exogenous phytase, the optimal dietary Ca level was verified. The 40-day study evaluated the effects of Ca level (4, 7 and 10g/kg diet) and Ca source (Ca from CaCO3 and from Lithothamnium calcareum) on mineral utilisation in 72 piglets (7.9±1.0kg BW) fed an exogenous phytase containing diet with 2.9g digestible P/kg. Measured parameters were growth performance, stomach mineral solubility, bone breaking strength and urinary, serum and bone mineral concentration. The apparent total tract digestibility of minerals was also assessed in the two diets with 7g Ca/kg, using 12 additional pigs. Regardless of Ca source, increasing dietary Ca impaired feed conversion ratio, increased urinary pH, increased serum and urinary Ca, decreased serum and urinary P, decreased serum Mg and increased urinary Mg, increased serum AP activity, decreased bone Mg increased bone Zn. Bone breaking strength was improved with 7 compared to 4g Ca/kg. Compared to CaCO3 , Ca from Lithothamnium calcareum increased serum Mg and with, 10g Ca/kg, it limited body weight gain. The dose response of Ca in a diet with 2.9g digestible P/kg and including exogenous phytase indicated that: (i) a low dietary Ca was beneficial for piglet growth, but was limiting the metabolic use of P; (ii) a high dietary Ca level impaired P utilisation; (iii) the optimal P utilisation and bone breaking strength was obtained with a dietary Ca-to-digestible P ratio of 2.1 to 2.4:1; (iv). Increasing dietary Ca reduced Mg utilisation, but not Zn status, when fed at adequate level. Finally, Ca from Lithothamnium calcareum had similar effects on Ca and P metabolism as CaCO3 , but impaired growth when fed at the highest inclusion level.