The objective of this experiment was to evaluate the effects of monensin on changes of fermentation pattern and resistance to intracellular potassium losses from ruminal bacteria of four cattle receiving high forage or high concentrate diets. The bacteria obtained by differential centrifugation were resuspended in a low potassium media. The intracellular potassium losses were measured after 10 minutes of incubation at increasing levels of monensin. The fermentation products were obtained after 24 hours of culture incubation with grass hay (100 mg/10 mL). Bacteria taken from cattle fed with 90% concentrate diet produced half as much methane and had 2-fold lower acetate to propionate ratio than bacteria from cattle fed forage. More monensin was required to decrease the methane production and the acetate to propionate ratio of bacteria from cattle fed 90% concentrate than bacteria from cattle fed forage. The amount of monensin needed to cause half of the maximal potassium intracellular losses in bacteria from animals fed 90% concentrate was 12-fold greater than the amount needed for bacteria taken from forage-fed cattle. Once those bacteria from forage-fed cattle are inherently more sensitive to monensin than bacteria from concentrate-fed cattle diets, a greater benefit of monensin on animal performance in high forage diets is expected.
bacteria; fermentation; intracellular potassium; methane; monensin; rumen
