With the aid of a labelled diagram, describe digestion in a named ruminant.

Named ruminant: Cattle (cow)

Digestion in cattle

1. The cow plucks grass, chews it only slightly and swallows it. The food is mixed with much saliva and passes through the oesophagus into the rumen and reticulum.
2. In the rumen, bacteria, protozoa and fungi ferment cellulose in the grass. These micro-organisms produce cellulase, which the cow itself does not produce. Some volatile fatty acids formed are absorbed through the rumen wall.
3. The partly fermented food is formed into balls called cud. During rest, the cud is regurgitated from the reticulum through the oesophagus to the mouth by reverse peristalsis.
4. In the mouth, the cud is chewed thoroughly and mixed again with saliva. It is then re-swallowed. This repeated chewing and swallowing is called rumination.
5. The re-swallowed food passes to the omasum. Its many folds grind the food further and absorb water and some mineral salts.
6. Food then enters the abomasum, the true stomach. It secretes hydrochloric acid and digestive enzymes, especially pepsin, which digest proteins, including proteins of the micro-organisms.
7. In the small intestine, bile, pancreatic juice and intestinal enzymes complete digestion. Digested nutrients are absorbed through the villi into the blood and lymph.
8. Some remaining fibre is acted upon by micro-organisms in the caecum and large intestine. Water is absorbed in the large intestine, while undigested residue is expelled through the anus as faeces or dung.