Figure 1

The rumen is the first chamber in the digestive system of ruminant animals, such as cows. The digestion of the cellulose rich feed of ruminants occurs through fermentation by microbes. The main substrates for the microbes are structural and non-structural carbohydrates (such as starch, hemicellulose and cellulose), which are hydrolysed into mono- or disaccharides by microbial enzymes. The resulting mono- and disaccharides are assimilated and fermented by the microbial community to volatile fatty acids (VFAs) which are absorbed into the blood stream by the ruminant, and are used as substrates for energy production and biosynthesis. The microorganisms eventually flow out into the omasum and the remainder of the digestive tract. The conditions in the rumen are favourable for the desired microbial community: anaerobic, weakly acidic pH between 5.3 and 6.7, solids content between 12 and 18%. The abomasum is strongly acidic (pH 2 to 4) therefore it acts as a barrier, killing the ruminal microbial flora. Finally, the microbial biomass is digested in the small intestine and smaller molecules (such as amino acids) are taken up by the ruminant.