You Are What You Eat
Animal Digestion

© Roger de la Harpe

Mouth Structure

What animals eat will indicate their main function among the diversity of species. Mouth structures have evolved to cope with the main diet of each species. We can, therefore, normally deduce what an animal eats, and thus its 'niche', by the structure of its mouth parts. Food is available in many forms and mouth parts must be adapted to gain access to each particular source. Where the supply is deep down, a long, uncurled probe is required ; where it is under a 'skin' a stiff, needle-like proboscis is required.

Paired jaws are commonly required for holding, chewing or cutting food. Long snouts are required to access food in some cases and these are often accompanied by long tongues. Wide opening mouths are required to access big food items, often accompanied by teeth suited for the job. Softer foods require sucking lips that can vacuum food while other food items require harder lips that can strip or pull food into the mouth. The variety is endless and more specific examples involving tooth, jaw, lip and tongue structure will be dealt with at a later time. It is enough here to encourage observation of the mouth structure of various animals. This will assist in working out what food they are adapted to eat and therefore what part they play in nature.

Animal Digestion

Once food is in the mouth it must be reduced, normally with the help of teeth, to a form that can be swallowed or ingested. Once the food is INGESTED it will normally enter a form of stomach where it is then DIGESTED. In the process of digestion the required nutrients and moisture are absorbed into the body systems and the excess matter is expelled from the body as waste matter. In most cases, stomach acids are effective in breaking down food matter into a form that can be absorbed. Foods that contain a high percentage of cellulose are immune to acids alone and require another treatment aided by BACTERIA.


RUMINANTS are animals that are normally cloven hoofed and have compound stomachs. Their intestines are unusually long (30 metres in sheep and 50 metres in cattle). This is necessary because of the slowness of vegetarian digestion. The food must pass through several compartments before reaching the intestine. These compartments are the RUMEN (or paunch), the RETICULUM (or honeycomb stomach), the PSALTERIUM (or manypiles) and finally the ABOMASUM (or rennet stomach).

The RUMEN is the largest compartment for storing hastily swallowed food. Rather like our shopping trolleys or baskets in a supermarket, it is used to gather and store food in rough form while out in feeding grounds where there is danger of attack. In this compartment there are spiky papillae which raise the temperature and promote bacterial fermentation that takes place there. This fermentation breaks down cellulose upon which digestive juices are ineffective. An offshoot of the RUMEN constitutes the 'honeycomb stomach', the intersecting folds of which form the RETICULUM.

The function of the RETICULUM is to assemble food in pellets ready for regurgitation, for the food has to go back into the mouth for RUMINATION, in which process it is ground to a pulp. Rumination, from which ruminants are classified, is done while the animal is at rest and may take several hours. This is rather like us taking our shopping home and then preparing and eating our meal in safety and comfort. If you see a giraffe standing (sometime lying) still and peaceful, watch it for a while and you will undoubtedly see it 'bringing up' its food and chewing it before swallowing it again.

You can see it travelling up and down the neck quite easily. The same, but not as obviously, with buffalo, impala, kudu and other ruminants. After RUMINATION the food is swallowed again and this time passes from the bottom of the gullet along a temporary fold in the stomach into the 'manypiles' or PSALTERIUM, which is lamellated like leaves of a book. Here the food is further broken down (triturated) before passing into the fourth and last compartment, the ABOMASUM or 'rennet stomach. This is a genuine stomach comparable to our own, in which the food is acted on by gastric juices. When a calf suckles, milk passes straight through to the 'rennet stomach' to be curdled and digested. Rennet tablets, obtained from the stomach of cattle, are what we use to make 'Junket' - or thick, curdled milk.


An important part of the whole digestive process is played by BACTERIA or what is termed stomach 'flora'. We have the same in our stomachs and if we take certain antibiotics we kill off the stomach flora and end up with an upset stomach. There is a compound - floralact - which one can take to reintroduce the necessary bacteria to get our digestion working again after antibiotic treatment. You may have noticed young animals - puppies etc - eating the droppings of other animals. This is 'natures' way of introducing the necessary bacteria into their new little stomachs to assist their digestion.

Adult animals do it as well and it is wise not to be too fastidious with human babies who have the same tendency. The bacteria in our stomachs are vitally necessary to our bodily functions and without them we would not survive. It is the same with wild animals - who have the tendency to defecate in waterholes etc, so that the necessary bacteria is passed on to others in the area. Bacteria are specific to certain food types and areas. Travellers will be well aware of the stomach troubles caused by change in diet and water supply.

Animals are also affected by having the wrong bactera when moved to a new area. In the normal course of events there would be a gradual change where they could pick up new bacteria as they moved along. With modern transport they are unable to affect this gradual change and end up in a new area with unsuitable bacteria in their stomachs. If there are already other animals in the area they will eventually pick up the necessary bacteria for that area and adapt. If they are moved to an area without other animals they will need to be treated with the correct bacteria for that area.

The 'lowveld' is an area of its own and there is no danger of transfers within such an area. I am talking about distance transfers between such areas as the 'Cape' , the 'Highveld', the 'Bushveld' , the 'Karroo' - basically between different 'biomes'. As I have mentioned before, it was well known to the 'voortrekkers' that new stock had to be 'dosed' with the stomach contents of a local animal before it would successfully digest and survive in a new area. Where have we lost this valuable knowledge?

Subsidised Feeding

With the common practice of importing expensive feed to subsidise overstocked populations, we should take care to ensure that animals have the correct ruminal flora to digest such introduced feed. I have seen a herd of impala, translocated from the highveld to a lowveld reserve, eating until they could burst, yet all dying of 'starvation' with full stomachs because they had the wrong ruminal flora and could not digest the food they had eaten. Attention should be paid to lowveld game populations that are being fed on feed imported from the highveld.

It does not all come contaminated with the right bacteria for its satisfactory digestion and it might be an idea to ask the suppliers to include some droppings from their local animals to mix in with the feed. Foot and Mouth would not be a worry from the highveld down to here. In any case our skilled veterinarians in the lowveld will be able to give you the right advice. If you notice animals eating subsidised feed but still starving despite what they are eating, check that they have access to the correct stomach flora - or bacteria.

Foot Note

What goes into your mouth becomes part of your temporary body. The excess passes out of the body to be recycled. For those content with reincarnation as some lower form of matter - so be it. Remember it is not what goes into your mouth that matters - but what comes out of it ! What goes into the eyes and ears stays in the soul to form lasting attitudes which direct our path to eternity. Those aware of eternal life would do well to watch the diet of their eyes and ears.

By Dave Rushworth

Kruger National Park - South African Safari