Monday, May 15, 2006


Herbivore “is an animal that is adapted to eat primarily plant matter (rather than meat)” (1). They can be classified into different sub-groups which include “the frugivores, which eat mainly fruit; or folivores, which specialize in eating leaves” (1).

Different plant foods are available differently depending on the variations of the seasons. As a result their diets tend to be different for example “in the temperate zones, where different plant foods are most available at different times of year” (1). “Many herbivorous animals that live in the temperate zones change their diet at different seasons of the year. In some places, some seasons are very rainy and wet, and others are very dry. Animals that live in these places may also change their diets at different seasons” (2).

There are the ruminants and non ruminants herbivores. “A ruminant is any hooved animal that digests its food in two steps, first by eating the raw material and regurgitating a semi-digested form known as cud, then eating the cud, a process called ruminating” (3). Goats, sheep, camels and girraffes are examples of ruminants. The stomachs of the ruminants are divided into four chambers i.e rumen, reticulum, omasum and abomasum.. “In the first two chambers, the rumen and the reticulum, the food is mixed with saliva and separates into layers of solid and liquid material. Solids clump together to form the cud (or bolus). The cud is then regurgitated, chewed slowly to completely mix it with saliva, which further breaks down fibers. Fiber, especially cellulose, is broken down into glucose in these chambers by symbiotic bacteria and protozoa” (3).

The non-ruminants (elephants) “digest carbohydrates, protein and fat by enzymatic action” (4). They can tolerate a diet of higher fibre content and lower nutritional quality. The non-ruminant has a lower digestive efficiency than ruminants and therefore a more rapid passage. The ruminants can take more food per time unit than a ruminant.

They vary of diets in these classes of herbivores poses some problems. These problems are normally seen during digestion. Some of the animals are unable to digest completely the food they eat. Cellulose is another source of problem and it contains much of the energy. Since most of the herbivores digest food through enzymes, therefore it is difficult for the enzymes to be broken down as it contains high organic substances. This cellulose composed of organic substances. only mechanical means such as extended chewing or fermetation can help to speed up the process of digestion.

However some animals overcome this problem through a quite a number of different ways. For instance ruminants able bring back food they ate to their mouth from their stomachs and chews again. “The rumen serves as a large vat in which the food, mixed with saliva, undergoes extensive fermentation - a slow decomposition of organic substances induced by micro- organisms. These micro-organisms are responsible for the breakdown of cellulose, the breakdown products becoming available for further digestion” (5)

“The fermentation products (mostly acetic, propionic, and butyric acids) are absorbed and utilized; carbon dioxide and methane (CH4) formed in the fermentation process escape by belching (eructation). Rumination, evident as "chewing the cud", involves the regurgitation and re-chewing of undigested fibrous material, which is then swallowed again. As the food re-enters the rumen it undergoes further fermentation. Broken-down food particles gradually pass to the other parts of the stomach where they are subjected to the usual digestive juices in the abomasums” (5).

“The rumen protozoans include ciliates which superficially resemble free-living forms such as Paramecium. Several hundred thousand protozoa are found in each millilitre of rumen contents. Many of the rumen organisms have been cultured in the laboratory, and extracts from pure cultures show cellulase activity. The ciliates are obligate anaerobic organisms which must meet their energy requirements through fermentation processes” (5).


1. Wikipedia contributors. Herbivore [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 23, 04:06 UTC [cited 2006 May 25]. Available from:

2. Wikipedia contributors. Herbivore [Internet]. Wikipedia, The Free Encyclopedia; 2006 Feb 16, 11:51 UTC [cited 2006 May 25]. Available from:

3. Wikipedia contributors. Ruminant [Internet]. Wikipedia, The Free Encyclopedia; 2006 Apr 22, 23:58 UTC [cited 2006 May 25]. Available from:

4. Wright, B. Equine Digestive Tract Structure and Function; 2006 May 03 UTC [Internet] [Cited 2006 May 25] Available from:

5. The gastrointestinal system, An introduction [Internet] [cited 2006 May 25]. Available from:

Mr Lufuno Mukwevho
CSIR Pretoria
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