Digestive strategies of small hindgut fermenters

ABSTRACT Small mammalian herbivores have a limitation in their supply system of nutrients to their energy and protein demands because they need much more energy and protein per unit body mass than larger herbivorous animals. Therefore, small herbivores need to have characteristic strategies in their digestive systems to overcome the limitation of their small body mass compared with larger animals. Although small herbivorous mammals commonly have an enlarged cecum, the pattern of flow and mixing of digesta in the large intestine varies among them. Distinct separation of the larger fiber particles from smaller and liquid contents which are retained in the cecum can be recognized in some species. Coprophagy, practiced by many small herbivores, has nutritional significance providing a source of vitamins, amino acids, and other nutrients which are excreted with feces. Among coprophagous mammals, several species produce two types of feces: soft feces, which are eaten; and hard, which are not eaten. Soft feces contain more water than hard feces and dry matter includes more protein and less fiber. Coprophagic behavior must be supported by the colonic separation mechanism, which operates retrograde transport of fluid and fine particle digesta or bacteria trapped in the mucus, resulting in high density bacteria in the cecum contents, which is successively consumed as cecotroph. These mechanisms must be necessary for small herbivores to survive on the feed in their habitat.