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How do ruminants digest?

Updated Friday, 30 August 2019
A quick introduction to how ruminants break down the plant matter they eat - equally useful as a quick revision aid on ruminants.

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What is a ruminant?

The word 'ruminant' is derived from the Latin word ruminare, to chew again. Ruminants are animals with four-part stomachs, which allows them to chew food more than once.

A ruminant's stomach

What is cud-chewing?

Cud-chewing  is an adaptation that enables many hoofed mammals to break down the cellulose of plant cell walls into nutrients that they can use and absorb.

What is the rumen?

The rumen is the first chamber of the ruminant's stomach.

What does the rumen do?

When a ruminant is feeding, it does so in a series of quick bites, giving the food no more than a cursory chew between its molar teeth, mixing it with large quantities of saliva (several hundred litres per day in domestic cattle) and then swallowing it into the first of the chambers, the rumen. Here powerful muscles churn it with the microbes that start the fermentation process. The food ferments, generating methane and carbon dioxide which are eructed. The microbes start to break down the cellulose of the cell walls into sugars, thereby releasing other nutrients from inside the cells. The microbes use some of these nutrients for their own metabolism, and in doing so generate fatty acids, which the ruminant can absorb into its blood through the wall of the rumen and can use in its own metabolism.

What does eructed mean?

Eructed basically means 'burped' - so when the animal's rumen has broken down the food into gas and solids, it will burp out the methane and carbon dioxide.

What is the reticulem?

The reticulem is the second chamber of the stomach.

What happens in the reticulem, and what are cuds?

Large pieces of plant material float on top of the fluid in the rumen and are passed to the reticulum, which has honeycomb partitions in its walls. Here the food is formed into balls called 'cuds'.

Eventually the animal takes a break from feeding, selects a resting place where it can keep watch for predators and spends some time ruminating - the cuds are regurgitated and the animal chews the material again, mixing it with saliva and breaking it down into smaller particles. This process gives a bigger surface area for the microbes to continue digestion of the food when it is swallowed again.

What is the omasum?

The omasum is the third part of a ruminant's stomach.

What happens in the omasum?

When the cuds have been broken down by chewing and the action of the rumen, material will pass into omasum. Here, muscular action breaks down the matter further.

What is the abomasum?

The abomasium - or true stomach - is the final part of the ruminant's stomach. Here, normal digestive enzymes get to work to break down the remains of the food and also to digest many of the microbes that have continued along with the food.

What happens to the remains of the food after it leaves a ruminant's stomach?

Digestion continues in the small intestine, and absorption of the digested food into the blood begins through the wall of the small intestine.

What is the caecum?

The caecum is the bulge from the side of the lower part of the animal's digestive tract.

What happens in the caecum?

Any material which has not been broken down by the process - especially tough plant material - has one further opportunity for fermentation, and absorption; this is in the caecum. Any material not digested by this stage in the process will be excreted from the body.  



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