Effects of calcium source, particle size and time on in-vitro calcium solubility of some indigenous Nigerian mineral ingredients for poultry diets

An experiment was conducted to investigate the effects of calcium source, and particle size on in-vitro solubility of seven different calcium sources available in Nigeria, namely calcium carbonate (42.84% Ca), bivalve shell (40.87% Ca), periwinkle shell (36.76% Ca), oystershell (39.19% Ca), eggshell (36.76% Ca), marble dust (39.85% Ca), and snail shell (36.05% Ca). Particle sizes were greater than 500 μ and less than 500 μ. Three different time periods were used, namely 10, 30, and 60 min. Calcium source and particle size significantly affected (P < 0.05) calcium solubility in 0.1 N HCl. Solubilities were: CaCO3, 99.99%; Bivalve, 87.35%; Periwinkle, 88.28%; Eggshell, 44.21%; Oystershell, 92.15%; Marble dust, 99.90%; Snail shell, 45.00%. There was significant interaction (P < 0.05) between calcium source and particle size for solubility for assays conducted over 10 and 60 min. Interaction effects generally show improved solubility, with reduced particle size, for the products of intermediate calcium solubility. X-ray diffraction showed that the calcium sources tested were all of the same mineral origin in terms of classification, i.e. calcite, although scanning electron microscopy revealed differences in the structures of the sources tested which may relate to solubility.