Veterinary advice: Four stomachs, but they don’t always work properly

A few recent cases of bloat have put me thinking about the stomach set-up in ruminants (cows, sheep, goats, etc).

In these animals, there are four stomachs.

Food and water comes in through the mouth and down the long pipe called the oesophagus and into the first stomach called the rumen.

At the bottom of the rumen is a sump-like pouch which is the second stomach, the reticulum. 

There is a short connection from here to the third stomach which is like a football, round and hard, called the omasum, and this is connected on to the fourth stomach called the abomasum.

What leaves the fourth stomach passes on into the small, and later, large intestines etc.

In the calf, in the first few weeks of life, the most important stomach is the fourth stomach. This is where the milk, which the calf drinks, is digested.

In young calves, there is a peculiar phenomenon by which the milk is diverted straight into the fourth stomach, thereby bypassing the rumen.

As the calf sucks, a reflex causes a channel or groove to appear from the end of the long pipe, the oesophagus, straight to the fourth stomach. Once here, the milk forms a clot which is then digested by the acids and enzymes in the abomasum.

Sometimes the digestive process goes wrong in the calf and we get a fermentation of the clot in this stomach.

This produces gas, and thus a bloat. This presents a problem to us, as we cannot pass a stomach tube down into this stomach to relieve the gas.

If we feed older calves by stomach tube with milk, this milk will end up in the first stomach, the rumen. The function of this stomach is to ferment its contents, usually grass and concentrates.

When milk comes in here, in the young calf, it just rots. The rumen is not yet functioning as a place of fermentation, because it has not developed.

This may cause a bloat in the rumen, but quite often, the rancid material passes on through the stomachs to the abomasum where it causes mayhem.

We will get a reddening of the inside lining of the abomasum because of excess acid production. This may well develop further to ulceration of the stomach lining, and perforation, which is fatal.

We often get a bloat here because of this, and the calf will become scoured. This kind of a scenario can also be caused by having poor milk hygiene, intermittent feeding of large volumes of milk, and feeding cold milk or milk replacer.

As the calf progresses from birth to weaning, the aim is to develop the rumen as a fermenting vat, so that it can hit the ground running when it is turned out to grass.

The calf needs a fully functioning rumen to break down the grass and concentrates. People sometimes take this for granted but the rumen and reticulum have a complex working system, with contractions happening once to three times every minute of the animal’s adult life.

These contractions mix up the grass, concentrates and water etc., they help belch up the gas, bring up cud for re-chewing and pass the broken down food on to the omasum.

Sometimes, there are problems here, and the gas is not belched back up, so the animal gets bloat. This may be caused by a piece of plastic or twine physically blocking the exit, or maybe the rumen has stopped turning. In any event, this is now an emergency that needs to be addressed immediately.

Frothy bloat is another day’s work, and one your local vet can explain to you.

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