Influence of lysocellin and monensin on mineral metabolism of steers fed forage-based diets.

Studies were conducted to determine the effects of lysocellin and monensin on mineral metabolism of steers fed forage-based diets. In each study treatments consisted of 1) control, 2) 100 mg lysocellin/d, 3) 200 mg lysocellin/d and 4) 200 mg monensin/d. Twenty-four growing Hereford steers were used in each of two experiments to evaluate the effects of ionophore feeding on plasma and ruminal soluble mineral concentrations. Steers were fed individually greenchop (tall fescue and bermudagrass) ad libitum and .91 kg/d of a corn-trace mineral salt-ionophore supplement. Plasma and ruminal fluid samples were obtained on d 28 and 84 in both studies. Ruminal concentrations of soluble phosphorus (P) and iron (Fe) were higher (P less than .05), whereas soluble manganese (Mn) was lower (P less than .01), in steers fed lysocellin than in controls. Steers fed lysocellin had higher (P less than .05) plasma magnesium (Mg) concentrations than control steers. Plasma and ruminal soluble mineral concentrations generally were similar for the monensin and 200 mg lysocellin treatments. Two additional studies were conducted to determine the effects of lysocellin and monensin on macromineral apparent absorption and retention in steers fed tall fescue greenchop. Steers were adjusted to their diets for 28 d and then placed in metabolism crates for a 6-d acclimation followed by a 5-d collection of urine and feces. Percent apparent absorption of calcium (Ca), potassium (K), Mg and P was higher (P less than .05), whereas sodium (Na) absorption was lower (P less than .05), in steers fed lysocellin than in controls. Mineral absorption was similar in steers fed 200 mg lysocellin or monensin. Calcium (P less than .05) and K (P less than .10) retention (percent of intake) was increased by ionophore feeding. Results indicate that lysocellin and monensin alter apparent absorption and retention of certain minerals in steers fed forage-based diets.