Influence of dietary calcium concentration on the digestion of nutrients along the intestinal tract of broiler chickens

The effects of dietary calcium (Ca) concentration on the digestion of Ca, phosphorus (P), nitrogen (N), fat and starch along the intestinal tract of broilers were assessed. Three-week old broilers were fed maize-soy diets containing 6, 9 or 12 g/kg of Ca (Ca: total P ratios of 1:1, 1.4:1 and 2:1, respectively) for six days and digesta were collected from the duodenum, jejunum, upper ileum and lower ileum. Apparent digestibility coefficients of P, Ca, N, fat and starch in different intestinal segments were calculated based on indigestible marker ratios in the diet and digesta. Apparent digestibility coefficients of P and Ca were determined to be negative in the duodenum. Apparent P digestibility was reduced (P<0.05) by increasing dietary Ca concentrations, but there was a Ca x intestinal site interaction (P<0.05). Jejunum was the major site of P absorption in birds fed the low Ca and normal Ca diets, but both the jejunum and upper ileum were involved in birds fed high Ca diets. Dietary Ca concentration had no effect (P>0.05) on apparent Ca digestibility. Calcium was absorbed predominantly in the jejunum. Digestibility of N and fat was reduced (P<0.05) by increasing dietary Ca concentrations. A significant (P<0.05) dietary Ca x intestinal site interaction was observed for N. In birds fed low Ca and normal Ca diets, N was primarily digested by the end of jejunum, but in birds fed high Ca diet both jejunum and upper ileum were involved. At all dietary Ca concentrations, fat was digested mainly in the jejunum and upper ileum, but digestion continued in the lower ileum. Apparent starch digestibility and AME were unaffected (P>0.05) by dietary Ca concentrations. Most of the starch digestion was completed by the end of the jejunum. The present data suggest that the site of digestion of P and N shifts depending on dietary Ca concentrations. Increasing dietary Ca concentrations negatively influenced the digestion of P, N and fat, but had no effect on those of Ca and starch.