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Digestion in Ruminan Speices:

Plant Material eg: Grass, Straw, leaves may contain large amounts of cell wall material containing fibrous carbohydrates, mainly cellulose and hemi-cellulose. Mammals and Birds do not produce the enzymes necessary to digest these components. However, the symbiotic micro organisms living in the alimentary tract can break them down. Ruminants have evolved to capitalise on this feature.

1. They exhibit special mastication and rumination processed to assist in the physical breakdown of herbage.

2. They have a large and complex four chambered stomach in which there is microbial fermentation of the food before gastric digestion takes place.

3. They have a well developed large intestine which acts as a second site of microbial fermentation, as in non ruminant herbivores.

Four Compartments of the stomach are: Rumen, Reticulum, Omasum and Abomasum.

Mastication is important in ruminants as it brings about physical breakdown of the food and exposes a larger surface area on which the cell wall digesting enzymes can work. Estimated that ruminants make between 40,000 - 60,000 chewing movements every 24hours.

Ruminants incisors are only present in the lower jaw and they bite against a hard dental pad on the upper jaw. The molar teeth are specialised for grinding the food. The different constitutes of the teeth wear away at different ways (the dentine wears before the cement before the enamel) the tooth soon becomes ridged with peaks of enamel and troughs of dentine. The peaks and troughs slide across each other during chewing so that the food between them is thoroughly macerated. The teeth continue to grow and regenerate as they are worn down. Chewing takes place in circular motions. The lower jaw moving from side to side across the upper jaw.

Rumination (Chewing the Cud). To regurgitate food into the mouth, the animal breaths in with the back of the mouth closed, which creates a low pressure in the oesophagus so that digesta can sucked up from the reticulum. Are liquids present are re swallowed and the solids re chewed. There is little chewing during grazing, the main chewing activity occurs later during the periods of rumination. This renewed chewing stimulates the secretion of saliva - important in assisting the mixing of digesta and by virtue the bicarbonate and phospate ions it contains of buffering the fermentation of food in the rumen. Ruminant animals secrete large volumes of saliva - up to 100 litres per 24hours in the cow.

First two compartments of the stomach are the reticulum and rumen - they form one continuous chamber (reticulorumen) but are distinguished by the ridged "honeycomb" projections on the inside surface of the reticulum and the small finger like projections (papillae) on the inside surface of the rumen.

Rumen functions as an ideal fermentation chamber - due to the constancy of conditions inside it (e.g: temperature, pH, volume of digesta) Able to support a vast population of bacteria and protozoa around 1010g and 106g rumen contents respectively. During the fermentation process, large volumes of gas are produced (e.g: 800 litres of carbon dioxide and 500 litres of methane per day per cow) If this gas is not removed, bloat will occur. Fatal as the rumen swells and eventually compresses the lungs and heart. Gas is normally removed by eructation. The Volatile Fatty Acids produced from breaking down the dietary fibre are absorbed through the walls of the reticulum and rumen.

The materials passing from the rumen to the lower gut comprise a mixture residues of feed and the bodies of microbes that have been produced in the rumen. Internal structure of the Omasum (third part of the stomach) has a series of muscular leaves. These absorb water and filter out large particles of plant material, ensuring these are retained in the rumen for a more prolonged period of fermentation. Periodically, the omasum contracts and liquid material is returned to the reticulum for further recycling, while the solid material is passed on to the abomasum.

Abomasum - Similar to the stomach of non ruminants. TRUE STOMACH

In the abomasum, small intestine and large intestine the pattern of digestion is similar to that in monogastric animals, although there are differences in the relative activities of the secreted enzymes and some specific adaptations that reflect the influence of the rumen fermentation process. Eg: because much of the fat flowing from the rumen consits of free fatty acids (as distinct from the neutral fat or triglyceride fat found in monogastric animals) ruminants have a distinctive mechanism to facilitate fat absorption. The bile is particularly rich in phospholipids (special type of fat) and the pancreatic juice contains both a lipase and a phospholipase. The latter attacks the phospholipid, releasing the powerful emulsifying agents (called lysolecithins), which act with the fatty acids in the digesta to form the micelles that are necessary for fat absorption.

In ruminant animals given forage diets, the large intestine acts as a second important site of microbial fermentation. As described in herbivorous monogastric animals, this results in VFA absorption and to a loss of microbial material in the faeces. Some ammonia absorbed from large intestine fermentation i the ruminant may be recycled to the rumen (via the formation of urea in the liver.) Under the correct circumstances, this may provide a useful nitrogen-conservation cycle.

In Newborn ruminants the reticulo-rumen is undeveloped and there is special mechanism, which allows milk to be channelled directly to the abomasum, where a distinctive peptidase, rennin is secreted. The oesophageal groove runs across in the wall of the reticulum from the base of the oesophagus to open at the top of the abomasum. The closed oesophaseal groove by-passes the rumen to allow more efficient digestion of milk. The walls of the groove are muscular and when stimulated to contract, curl up so that the groove becomes a tube and can carry liquids (i.e, milk.) from oesophagus to abomasum. Closing of the groove is a reflex action and works most efficiently when the young ruminant is sucking rather than drinking.

As the young animal develops and begins to eat solid food the rumen develops in size , the fermentaion function becomes established and the ooesophagael groove reflex is not utilised. Liquids given through a dosing bottle have shown that under these circumstances the oesophagael grove reflex can be retained well after weaning.

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