Apparent ileal digestibility of calcium in limestone for broiler chickens

• Apparent ileal digestibility of calcium in limestone was determined in broilers using the direct method.
• Calcium digestibility coefficients of the three limestone samples ranged from 0.54 to 0.61.
• Increasing the dietary phosphorus concentration from 0 to 4.5 g/kg increased the apparent ileal calcium digestibility of limestone from 0.56 to 0.60.
• Further studies are needed to determine the calcium digestibility of other commonly used calcium sources.

The objective of the study that is presented herein was to determine the apparent ileal calcium (Ca) digestibility of limestone for broiler chickens as influenced by limestone source and dietary phosphorus (P) concentration. Limestone from three commercial sources (coded as LM-1, LM-2 and LM-3) were obtained, ground to pass through a 0.2 mm sieve and analysed for mineral composition and in vitro solubility. Analysed Ca concentration and in vitro solubility coefficient of LM-1, LM-2 and LM-3 were 410, 390 and 420 g/kg, and 0.28, 0.29 and 0.27, respectively. Two experimental diets, containing 9 g/kg Ca, were developed from each limestone source with 0 and 4.5 g/kg dietary P. Titanium dioxide was incorporated as an indigestible marker. Each experimental diet was then randomly allotted to six replicate cages (eight birds per cage) and fed from day 21 to 24 post-hatch. Apparent ileal digestibility of Ca was calculated using the indicator method. Apparent ileal Ca digestibility coefficients of LM-1, LM-2 and LM-3 were determined to be 0.58, 0.61 and 0.54, respectively. Calcium digestibility of LM-3 was lower (P < 0.05) than LM-2 but similar (P > 0.05) to LM-1. There was no difference (P > 0.05) between the Ca digestibility of LM-1 and LM-2. Increasing the dietary P concentration from 0 to 4.5 g/kg in assay diets increased (P < 0.05) the average Ca digestibility from 0.56 to 0.60.