The effect of monensin on in vitro utilization of lactate in the rumen contents

The effect of monensin on the in vitro utilization of lactate in the rumen contents of a steer, cow and two wethers was investigated. The rate of the utilization of lactate in monensin-treated cultures was on average only two thirds of that found in cultures without monensin. Monensin tended to increase acetate and to decrease butyrate in cultures with lactate. After 11-week adaptation of a wether to monensin the inhibitory effect of ionophore persisted, being, however, less pronounced and without influence on the molar percentages of VFA. Effects of monensin reported here seem to be caused by its inhibiting action against rumen lactilytic protozoa. There were no significant differences between monensin from Elanco and the Czechoslovak analogue.