Polysaccharide Degradation in the Rumen and Large Intestine

The rate and extent of degradation of plant structural tissues during digestion depends on a combination of animal, plant, and microbial factors. The major animal effect is the nature of the digestive tract itself. Ruminants with pregastric ruminai fermentation generally have a lower rate of passage than is seen in monogastric animals, and rumination (regurgitation and remastication) of large particles permits them to macerate fibrous materials more completely than do monogastric animals. Ruminants are thus more efficient at digesting fibrous plant material than are monogastric animals, in which fermentation occurs only in the large intestine. In contrast to ruminants, monogastric animals often tend to consume more readily digestible feeds. For example, cereals are a major component of the diets commonly fed to domestic animals. Thus, there is often a quantitative compositional difference in the substrates available to the digestive microbiota present in ruminants and monogastric animals. Cellulolytic organisms which are of pivotal importance in the rumen are generally viewed to have a lesser role than other fermentative organisms in the postgastric intestinal fermentation of domestic animals; however, there are exceptions — for example, the horse. Undoubtedly the presence or absence of particular gut species is directly related to the diet consumed and the retention time of the system.