Hind-Gut Fermentation

By Art de Lamerens

[Originally written as a response to a question on the TortoiseForum.Org. Reprinted with permission.]

Coprophagy (the consumption of feces) is practiced by young torts to establish intestinal flora necessary for the digestion of food materials particularly cellulose. Typically, adult torts do not consume their own or other torts’ (of the same species) feces. They will consume other animals feces as a protein or nutrient source and just to gross out their owners!

In response to a comment made about many hind-gut fermenters that eat their own feces and need to do so for health:

The “double-whammy” or “recycling”, otherwise known as caecotrophy, is the production of partially digested pseudo-fecal (caecal) pellets which are excreted and immediately consumed. It is limited to a few high metabolism organisms like rabbits, hamsters and certain other small mammals. The digestive product of caecal pellets are feces which are not consumed. This mechanism evolved to eliminate prolonging the digestive process necessary for fiber fermentation, reducing the load in the digestive tract and still be able to utilize the nutrients generated by the shorter fermentation. True caecotrophs will starve to death if prevented from consuming the caecal pellets.

On “hind-gut fermentation” as a method of digesting fiber better:

Cellulose is a structural constituent of plant cell walls. In certain parts and types of plants the cellulose serves as “armor”. Vertebrates are incapable of producing cellulase (notice the “A”), the enzyme responsible for breaking down (digesting) cellulose. Certain microbes in the intestinal flora of many animals, even termites, can produce cellulase and in most herbivores are harbored within the intestines for this purpose.

Fiber (cellulose) itself is not absorbed during digestion. It is actually a barrier to digestion. The purpose of chewing, foregut fermentation by ruminants, acid hydrolysis in the stomach and hind-gut fermentation in
many higher animals is an attempt to release and/or convert released nutrients from within the plant cells and convert some of the cellulose (via microbial action) into useable nutrients.

Tortoises, in general, have a rather slow digestive process. The purpose of the slow digestion is to allow time for the microbial digestion of the plant cell walls so as to release the nutrients within and the production of additional nutrients by the microbes themselves for absorption in the colon like certain B vitamins, vitamin K and fatty acids. The amino acids, proteins and certain other nutrients generated by these microbes are mostly lost as there is no means for them to be absorbed in the posterior (distal) colon.

Overall, hind-gut fermentation does not generate great quantities of nutrients responsible for energy production. Although up to 30% may occur in the anterior (proximal) and mid colon, the majority occurs in the small intestines and “functional” caecum (an eccentric dilation of the anterior colon in tortoises). The relatively low energy available precludes hind-gut fermentation from providing long-term sustenance. In
almost all cases, prolonged activity during periods of extended fasting is fueled by fat reserves.

The research that demonstrates a direct correlation between fiber content and digesta retention time simply illustrates that low fiber (greens, fruits, flowers, shoots, etc.) diets, similar to our own, do not require substantial cellulose fermentation whereas higher fiber (grasses, sedges, twigs, etc.) diets do. Higher fiber diets reduce the average digestibility (the amount utilized vs. the amount eaten) as well – the expected scenario for most tortoises. Tortoises, among others, are able to modify the rate at which digesta move through the colon, including reverse peristalsis in some instances, thereby maximizing the efficiency of the fermentation by retaining the materials in the digestive tract longer.

Eating daily does not equate to excreting daily necessarily. Once digested, the large masses of material are reduced considerably in volume: most food items are largely composed of water which is absorbed. The
utilized components of the diet comprise a surprisingly small percentage of the total mass consumed. Depending upon the food materials consumed defecation may occur from once every several days to
multiple times per day.

Read more: http://www.tortoiseforum.org/Thread-Benefit-of-Hind-Gut-Fermentation

Revised 11-28-2011 (C) Art de Lamerens,