Propionate Production in the Rumen of Holstein Steers Fed Either a Control or Monensin Supplemented Diet

Rumen propionate production in steers fed either a control or monensin supplemented diet was measured by an isotope dilution technique. The feeding of the control ration (5.9 kg hay, 2.5 kg concentrate) gave a typical high acetate type fermentation, while supplementing the same ration with monensin at a level of 33 ppm significantly increased the molar proportion of rumen propionate (19.1 vs 24.7%). Monensin supplementation increased propionate production from 7.74 moles/day to 11.18 moles/day. These results show that the change in the molar proportions of the volatile fatty acids resulting from monensin supplementation can be explained on the basis of an increase in propionate production.