plant-eating animals with the celebrated multiple-chambered stomachs. Herbivorous animals that eat a diet of relatively soft vegetation do not need a multiple-chambered stomach. They typically have a simple stomach, and a long small intestine. These animals ferment the difficult-to-digest ﬁbrous portions of their diets in their hindguts (colons). Many of these herbivores increase the sophistication and efﬁciency of their GI tracts by including carbohydrate-digest- ing enzymes in their saliva. A multiple-stomach fermentation process in an animal which consumed a diet of soft, pulpy vegetation would be energetically wasteful. Nutrients and calories would be consumed by the fermenting bacteria and protozoa before reaching the small intestine for absorption. The small intestine of plant-eating animals tends to be very long (greater than 10 times body length) to allow adequate time and space for absorption of the nutrients.

Colon

The large intestine (colon) of carnivores is simple and very short, as its only purposes are to absorb salt and water. It is approximately the same diameter as the small intestine and, consequently, has a limited capacity to function as a reser- voir. The colon is short and non-pouched. The muscle is dis- tributed throughout the wall, giving the colon a smooth cylindrical appearance. Although a bacterial population is present in the colon of carnivores, its activities are essen- tially putrefactive. In herbivorous animals, the large intestine tends to be a highly specialized organ involved in water and electrolyte absorption, vitamin production and absorption, and/or fer- mentation of ﬁbrous plant materials. The colons of herbi- vores are usually wider than their small intestine and are rel- atively long. In some plant-eating mammals, the colon has a pouched appearance due to the arrangement of the muscle ﬁbers in the intestinal wall. Additionally, in some herbivores the cecum (the ﬁrst section of the colon) is quite large and serves as the primary or accessory fermentation site.

What About Omnivores?