How Does Rumination Work?

You undoubtedly know that cattle, sheep, and goats are considered ruminants, that they have multiple stomachs, and that they chew their cuds as part of the digestive process.

Well, that’s just the simplified version of what is actually going on.  Rumination is an incredibly sophisticated process.  Here’s a little more information:

1. The animal swallows a mouthful of grass or other plant matter.  Very little chewing takes place at this stage.
2. Since the mouthful of food is still pretty much intact, it must be broken down further.  It goes to the rumen, the first part of the stomach, to begin fermentation.
3. Large, inedible objects, like rocks and nails, are trapped in the reticulum, the second part of the stomach, and settle to the bottom.
4. The contents of the rumen mix and settle into three layers.  Gases released from fermentation are on top, newly arrived forages float in a mat in the middle, and older, fluid-saturated forages are on the bottom.
5. The rumen gradually releases large, floating particles from the middle layer into the reticulum for further digestion.  (The rumen and reticulum share their contents fairly freely.)
6. In the reticulum, microorganisms break down the food further, forming cuds.
7. While the animal is resting, it brings the cuds back up to be chewed and mixed with saliva, aiding the process of digestion.
8. When the cud is swallowed again, it goes back to the reticulum.
9. The liquid parts of the cud go to the omasum, the third part of the stomach.
10. The solid parts of the cud go back to the rumen, forming the bottom layer of forage mentioned in step 3.  Microbes in the rumen use this mat of old forage to make energy to carry out the fermentation process and digest the newer forage on top.
11. As fermentation progresses, the more fully digested liquid parts of the material at the bottom of the rumen return to the reticulum for transfer to the omasum.
12. Scientists do not fully understand the function of the omasum, but it appears to absorb water and some nutrients from the food.  It probably also filters out larger particles to prevent them from proceeding further without further digestion.
13. The food next goes to the abomasum, the fourth and final part of the stomach, where it is mixed with gastric juices that break the more complex nutrients down for absorption by the intestines.  This part of the stomach works just like the stomach in non-ruminant animals.
14. The food passes out of the stomach and into the intestinal tract for nutrient absorption.

Of course, this is still a simplified explanation of rumination.  Different types of nutrients are broken down and absorbed in slightly different ways, and different feedstuffs also have different effects on the ruminant digestive system.  Add to this the variations between different species, and we start to see what an intricate process rumination really is!