Determination of apparent and true ileal digestibility of calcium in limestone with different particle sizes in broilers and pullets

A feeding experiment was performed to determine the effect of limestone particle size on apparent (AIDC) and true (TIDC) ileal digestibility coefficients of calcium (Ca) in broilers and pullets. With this motivation, four dietary treatments were developed based on a 2×2 factorial arrangement, that included two limestone particle sizes (fine vs. coarse) and two bird types (broilers vs. pullets). Each treatment was replicated six times (eight birds/replicate). Two corn-based diets containing limestone with either fine (<0.5 mm) or coarse (1-2 mm) particles as the sole Ca source were developed and fed to broilers and pullets from 16 to 20 days of age. A Ca-unsupplemented diet was used to determine the ileal endogenous Ca losses. Titanium dioxide was incorporated in all diets as an indigestible marker. Digesta were collected on day 20 from all birds per pen. The AIDC of Ca was determined by marker and the TIDC values were determined by correcting for endogenous Ca losses. Endogenous Ca losses were obtained to be 420 and 696 mg/kg of dry matter intake for broilers and pullets, respectively. Broilers consumed more feed (P=0.001) and had higher body weight gain (P<0.05) than the pullets. Broilers had higher AIDC and TIDC of Ca than pullets (P<0.001). Coarse limestone particles increased the AIDC and TIDC of Ca regardless of bird type. Feeding coarse limestone increased the Ca concentration in the gizzard content of broilers but not in pullets, resulting in a significant (P<0.05) interaction between limestone particle size and bird type. Regardless of bird type, increasing limestone particle size enhanced AIDC and TIDC of Ca in limestone.