With the objective of evaluating increasing levels of calcium in diets supplemented with the enzyme phytase for chickens from 1 to 21 days of age, an experiment was conducted using 600 1-d old Hubbard-MPK strain chicks. The broilers were allotted to a completely randomized 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 phosphorus and 600 units of phytase/kg, was formulated to meet the nutritional requirements of the broilers, according to NRC (1994), except for calcium, whose levels were 0.46; 0.67; 0.88; 1.09 and 1.30%. At 14 days, two chicks of each treatment were transferred to metabolism cages for total collection of the excreta during four consecutive days. At 21 days of age, two broilers from each treatment were slaughtered for removal of the left tibia for subsequent analyses. The males presented higher fed intake and weight gain, and shown a linear reduction as the level of calcium was increased. The levels of 0.67 and 0.71% presented better digestibility of dry matter and higher nitrogen retention, respectively. The females presented content of ashes and calcium in the tibia higher than those of males (1.68 and 2.34% respectively). The level of 0.55% of calcium in the diets provided the maximum deposition of ashes (51.5%) while the level of 0.59% was enabled to reach the maximum calcification (17.8%). Phosphorus deposition showed quadratic effect in relation to increasing levels of calcium in the diets, and 0.75% of calcium provided to reach the largest deposition (10.8%), while deposition of manganese was reduced linearly with the increasing levels of calcium in the diets. It was concluded that high levels of calcium in the diets supplemented with phytase decreased weight gain and shown negative effect on the phosphorus and manganese deposition in the broilers tibia from one to 21 days of age. Low levels of calcium impaired the digestibility of dry matter and nitrogen retention of diets of broilers one to 21 day old broilers.
digestibility; performance; phosphorus; requirement; ash; manganese; mineralization; zinc
