Effect of monensin on fermentation pattern and soybean protein degradation in the rumen of sheep

The effect of a daily dose of 30 mg Monensin on rumen fermentation pattern and degradation of the crude protein fraction of soybean meal was investigated with sheep. Degradation parameters for soybean meal were measured by the nylon bag technique. Monensin increased propionic acid percentages in the rumen, with a concomitant decrease in acetic- and butyric acid proportions, thus confirming earlier work. Ammonia N concentration in the rumen was also lowered, indicating an inhibitory effect on rumen protein breakdown. However, no effect on degradation rate, degradability and effective degradability (only with one sheep) could be observed. Possible reasons for these findings are discussed. Amino acid analysis on the residues in incubated bags revealed slight changes in amino acid composition, but these changes were considered to be nutritionally unimportant.