Comparative aspects of digestion in the hindgut of mammals. The colonic separator mechanism (CSM) (a review)
Björnhag, G.
Deutsche Tierärztliche Wochenschrift 94(1): 33-36
1987
ISSN/ISBN: 0341-6593 PMID: 3545761 Document Number: 290513
Small animals have mostly a high metabolic rate. They need a rapid release of nutrients from food but this results in a short retention time for food, especially when digestibility is low. Herbivores use microorganisms for fermentation of the coarse food. In small herbivores the time needed for multiplication of the microorganisms is mostly longer than the mean retention time of the food. These animals have evolved mechanisms to retain the microorganisms for a sufficiently long time. Several mammalian species with hindgut fermentation use colonic separation mechanisms (CSM) for that purpose. Different types of CSM are described for myomorph rodents, caviomorph rodents, lagomorphs, some marsupials and equines. The two groups of rodents studied utilize a CSM strategy resulting in longer retention time for bacteria than for food. The bacteria are separated from the food in the proximal colon and are transported in retrograde direction towards and mostly into the caecum. The other animals use a CSM strategy retaining not only microorganisms but also water and small food particles. The latter are mostly of high digestibility. This separation also occurs in the proximal colon and the fine matter is retained in the caecum or the proximal colon.