Source: Nature: "Holy Cow"
Major corporate support for the Nature collection was provided by Canon U.S.A. and SC Johnson. Additional support was provided by the Corporation for Public Broadcasting and the nation’s public television stations.
Cows are ruminants, animals with a unique digestive system that allows them to live on otherwise unpalatable foods by repeatedly regurgitating and rechewing them as "cud." The cud is then swallowed again and further digested by specialized bacterial, protozoal and fungal microbes that live in the rumen, one of the four compartments of a cow's stomach. Learn more about a cow's digestive system in this video segment from Nature.
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Cattle originally evolved over millions of years through a process of natural selection-also known as “survival of the fittest”-which made them adaptable to a wide variety of environments, including most of those inhabited by another highly adaptable species: humans. Once humans discovered how to domesticate cattle about 4,000 years ago, they began to selectively, or “artificially,” breed them for specific desired traits like meat and milk production. This resulted in animals fit less for survival in the wild than the satisfaction of human needs, but in purely genetic terms, the arrangement has proven highly successful for cattle. Cattle now thrive throughout the world in over 800 different breeds, each more or less successfully adapted to their environment and the needs of their human caretakers.
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.
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