Effects of calcium carbonate supplementation on Ca, Mg and P metabolism in ewes.

Abstract

A mineral balance (Ca, Mg and P) was examined in five non-pregnant ewes that had been fed on a fixed ration for 10 days (C-1 period), the ration supplemented with calcium carbonate (CaCO3;750 mg/kg b.w.) for the following 14 days (E period), and again the ration solely for the last 7 days (C-2 period). Increased dietary Ca content (E period) resulted in significant increases in the apparent absorption and retention of Ca, but the urinary excretion of Ca did not change and the serum concentration of Ca rose only transiently and slightly. High dietary Ca content resulted in gradual increases in the fecal excretions of Mg and P, and consequently in decreases in the apparent absorptions and retentions of them. Though the urinary excretion of Mg did not change, that of P increased, especially in the last half of E period, and after this the retention of P showed a negative value. The serum concentration declined transiently in Mg and rose transiently in P regardless of their balances. In C-2 period, the apparent absorption and retention of Ca showed negative values, but the urinary excretion and serum concentration of Ca did not change. The apparent absorption and retention of Mg were decreased by increased fecal and urinary excretions of it, and the serum Mg level remained low. Though the apparent absorption of P increased, there was only a slight positive retention of P because the urinary excretion rate of P remained high. These results indicate that the transient increase of Ca absorption resulted from high dietary Ca content inhibits metabolisms of both Mg and P.