JOHN WEBSTER: The key to the cow’s success lies here, the rumen. It’s sort of the belief of every school child that the cow has four stomachs, that’s not really true, what it has is one true stomach the abomasum which is exactly the same as our stomach. Upstream of that is a multi-compartmental fermentation vat, fermentation chamber wherein live the microbes
JOHN WEBSTER: Now when the cow goes out to graze she eats the grass really as quickly as possible and swallows it almost unchanged. That comes into the rumen and at that point it’s really quite difficult for the microbes to penetrate through the cell wall and start the chemical digestion of the plant fiber.
So what the cow has also evolved is this really elegant mechanism of rumination. In this she moves the food round in the rumen and then a bolus of food is regurgitated, passes up to the mouth and then she takes it in her mouth and chews it rather as old cowboys would chew tobacco: 20 chews on one side 20 chews on the other. This breaks it up and it comes back again into the rumen
The microbes, having done their work then are passed out of the fermentation chamber into the abomasum where they heroically die and give up their lives to provide protein for the cow to produce milk and meat for ourselves.