INFLUENCE OF SODIUM-BICARBONATE AND MONENSIN ON UTILIZATION OF A FAT-SUPPLEMENTED, HIGH-ENERGY GROWING-FINISHING DIET BY FEEDLOT STEERS

Two feedlot growth performance trials and a metabolism trial were conducted to evaluate the relationship between monensin (MON) and sodium bicarbonate (BICARB) supplementation on utilization of a high-energy diet by finishing steers. Two levels of MON (0 and 33 mg/kg of diet) and two levels of BICARB (0 and .75% DM) were compared in a 2 x 2 factorial arrangement of treatments. The basal diet contained 75% steam-flaked corn, 4% yellow grease, and 12% forage (DM basis). There were no interactions between supplemental BICARB and MON on feedlot growth performance or characteristics of ruminal and total tract digestion. With either crossbred or Holstein steers there were no treatment effects (P > .10) on ADG, DM intake, feed efficiency, or NE value of the diet. The BICARB did not influence (P > .10) ruminal or total tract digestion of OM, ADF, starch, and N, ruminal pH, or ruminal VFA molar proportions. Monensin decreased (6.6%, P < .10) ruminal OM digestion. However, differences in ruminal digestion were compensated for by increased (3.2%, P < .05) postruminal OM digestion. Effects of MON on total tract digestion of OM, ADF, N, starch and GE were small (P > .10). Monensin decreased ruminal molar proportions of acetate (5.3%, P > .10) and butyrate (29.4%, P < .05) and increased molar proportions of propionate (16.3%, P < .10). Coupled with reduced ruminal OM fermentation, the increase in molar proportions of propionate caused a decrease in ruminal methane energy loss and increased diet ME (2.7%, P < .05). It is concluded that the growth performance responses to supplemental MON and BICARB may be small in fat-supplemented, high-energy finishing diets. The absence of either a MON or BICARB main effect on growth performance precludes conclusions about the potential for an interaction.