Effect of Monensin or Lasalocid, with and without Niacin or Amicloral, on Rumen Fermentation and Feed Efficiency

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Abstract
A series of in vitro studies tested the effects on rumen fermentation of monensin sodium, lasalocid sodium and Polyether A (an experimental antibiotic) with and without niacin or amicloral. Monensin and lasalocid, at concentrations between 11 and 66 ppm, depressed microbial protein synthesis; the effect of Polyether A at 11 to 66 ppm was not so severe. However, all three antibiotics at 176 ppm severely inhibited protein synthesis. Niacin enhanced, but amicloral depressed, protein synthesis. Both monensin and lasalocid increased rumen propionic acid concentration and decreased acetic. None of the three antibiotics affected total volatile fatty acid concentration. Monensin increased rumen lactate. Monensin and lasalocid inhibited gas production and decreased rumen methane production. Holstein heifers were used to compare the effects of 33 ppm monensin, 11 or 33 ppm lasalocid, and 11 or 3 3 ppm Polyether A. An extra rumen fistulated cow in each group provided rumen fluid for analysis. None of the antibiotics affected weight gain (168 days). Each reduced feed intake and improved feed efficiency. The largest decreases in rumen acetic acid and largest increases in rumen propionic acid resulted from 33 ppm of monensin or lasalocid. We concluded that lasalocid behaves like monensin in regard to rumen fermentation and feed efficiency. Copyright © 1979. American Society of Animal Science . Copyright 1979 by American Society of Animal Science.