1. In a 42-d feeding trial, 264 one-d-old, as hatched, Cobb 400 broiler chickens (6 pens per group, n = 11 per pen in a 2 × 2 factorial arrangement) were fed on two concentrations of
dietary calcium (Ca) (9.0 and 7.5 g/kg in starter, 7.5 and 6 g/kg in grower phases) and supplemental
phytase (0 and 500 U/kg diet). 2. During d 0-21, the high Ca +
phytase diet improved
body weight. During d 0-42, feed intake was increased by the low Ca diet and decreased by
phytase supplementation. Feed conversion ratio during d 0-21 was improved by the high Ca +
phytase diet. 3. At d 42, Ca in duodenal digesta was reduced by low dietary Ca and supplemental
phytase. High dietary Ca reduced P in duodenal and jejunal digesta.
Phytase reduced digesta P and increased serum P concentration. 4. Relative tibia length decreased with low dietary Ca and increased with
phytase. The robusticity index of tibia was improved by the low Ca diet and
phytase supplementation.
Phytase supplementation increased tibia ash and concentrations of Ca,
magnesium (Mg),
manganese (Mn),
copper (Cu),
zinc (Zn) and
iron (Fe) in tibia. The low Ca diet increased Mg, Mn and Fe and reduced Cu and Zn in tibia. 5. It was concluded that 7.5 g Ca/kg during weeks 0-3 and 6 g Ca/kg during weeks 3-6 sustained broiler performance and
bone ash, while
phytase supplementation facilitated tibia mineralisation, particularly during the grower phase.