The objective of this work was to study the calcium metabolism in growing equines receiving diets with different calcium levels. Twelve male were used, with average age of twelve months and average alive weight of 221,0 kg. The treatments consisted of three diets, composed for increasing calcium levels (low = 0.15%-N15; standard = 0.45%-N45; high = 0.75%-N75), and standard phosphorus level (0.23%). Each animal was injected, through the right jugular vein, the volumes of a syringe, which corresponded to about 7.4 MBq of 45Ca (CaCl2). After the injection, blood samples (10 mL) were collected through left jugular vein at five minutes, 1, 2, 4, 6, 24, 48, 72, 96, 120 and 144 hours. The feces were daily collected in the morning, 24 hours after the application of the radionuclide until the seventh day, and an aliquot of 5% of the daily total excreted was collected and stored in freezer for posterior analysis. The same procedure of excrements was adopted for urine, when samples of 1% of the daily total volume had been collected. The experimental techniques used a completely randomized design with three treatments and four replications. No effects were observed on the plasma calcium, total calcium in urine and endogenous calcium in feces, with average values of 11,76; 5,54 and 20,86 mg/kgLW/day, respectively. No effects were observed for the biological calcium availability, with 81.67%, on average. Linear regressions between calcium levels in the diet and total calcium ingested, absorbed calcium, total calcium in feces and restrained calcium have been respectively verified, which were expressed according to the following equations: y=10.7+2.78x r²=1.0; y=12.41+2.24x r²=0.99; y=5.97+0.92x r²=0.93 and y=6.4+1.70x r²=0.94, with averages of 135.80; 113.21; 47.37 and 82.90 mg/kgLW/day, respectively.
homeostasis; horses; mineral; radioisotopic
