With the objectiveof evaluating increasing levels of calcium in diets supplemented with the enzymephytase for chickens from 1 to 21 days of age, an experiment was conducted using600 1-d old Hubbard-MPK strain chicks. The broilers were allotted to a completelyrandomized design, factorial arrangement five x two (levels of calcium x sexes),three replicates and 20 birds per plot. The basal ration with 0.54% total phosphorusand 600 units of phytase/kg, was formulated to meet the nutritional requirementsof the broilers, according to NRC (1994), except for calcium, whose levels were0.46; 0.67; 0.88; 1.09 and 1.30%. At 14 days, two chicks of each treatment weretransferred to metabolism cages for total collection of the excreta during fourconsecutive days. At 21 days of age, two broilers from each treatment were slaughteredfor removal of the left tibia for subsequent analyses. The males presented higherfed intake and weight gain, and shown a linear reduction as the level of calciumwas increased. The levels of 0.67 and 0.71% presented better digestibility ofdry matter and higher nitrogen retention, respectively. The females presentedcontent of ashes and calcium in the tibia higher than those of males (1.68 and2.34% respectively). The level of 0.55% of calcium in the diets provided themaximum deposition of ashes (51.5%) while the level of 0.59% was enabled toreach the maximum calcification (17.8%). Phosphorus deposition showed quadraticeffect in relation to increasing levels of calcium in the diets, and 0.75% ofcalcium provided to reach the largest deposition (10.8%), while deposition ofmanganese was reduced linearly with the increasing levels of calcium in thediets. It was concluded that high levels of calcium in the diets supplementedwith phytase decreased weight gain and shown negative effect on the phosphorusand manganese deposition in the broilers tibia from one to 21 days of age. Lowlevels of calcium impaired the digestibility of dry matter and nitrogen retentionof diets of broilers one to 21 day old broilers.
