The rumen, as the first chamber of a ruminant's multiple-chambered stomach system, acts as a fermentation chamber to break down the plant fibers that make up the majority of the diet. The microbial population of a rumen must balance lactate-producing bacteria to be effective.
This balance of the rumen's bacteria requires a proper mixture of fiber, energy, water and nitrogen. When imbalanced, the pH of this organ, dependent on the health of the bacterial inhabitants, leads to acidosis and improper digestion. After plant fiber is thoroughly fermented in this gut, it is, along with the bacteria, moved into the second chamber, the abomasum. The bacteria act as a protein source for the largely plant-based ruminant diet.