Production and metabolism of volatile fatty acids, glucose and CO2 in steers and the effects of monensin on volatile fatty acid kinetics.

A study was conducted to determine effects of monensin supplementation on production and interconversion rates of rumen acetate, propionate, and butyrate and plasma acetate. Measurements were made by isotope dilution techniques in four Holstein steers fed a 70% alfalfa hay, 30% corn ration. In addition, a general kinetic method for solution of open systems has been applied to quantify metabolism of the rumen volatile fatty acids and glucose and the production of CO2. Dietary monensin increased rumen propionate production at the expense of rumen acetate production so that total volatile fatty acid production was unchanged. Butyrate production tended to increase, indicating that decreased acetate production may result in diversion of hexose to propionate and butyrate production and direction of reducing equivalents away from methane production. These changes were calculated to increase rumen fermentation efficiency by 6%. Oxidation of the rumen volatile fatty acids and systemic plasma glucose accounted for only 35% of CO2 production.