Cows create gas during the digestion process. They eat mostly plant materials, like grass, hay, or grains, and because they chew, chew, chew, are able to break down plant fiber and use the complex sugars that are trapped in the tough stems. This constant chewing is called rumination. To see a demonstration of rumination, see the video "Moo Tube", (this video takes a little time to load and play, be patient)! While the cows chomp away, saliva flows into their mouths. The saliva is full of enzymes that also help break down the plant cells.
As the cow chews, the food rolls into a little ball called a bolus or cud.
Cows have one big stomach with four compartments or chambers. When the cud is swallowed, it moves down the cow’s throat through a long tube called the esophagus and into the first chamber of the stomach called the rumen.
The rumen is filled with thousands of microorganisms (bacteria, protozoa, & fungi.) They break down the cellulose in the plant stems. Since these little microorganisms don’t have teeth, they are only able to break down the surface area of the food particles. To expose more edible area for the bacteria, the cow regurgitates the cud to chew it some more and then swallow it again. As the microbes eat the foodstuff, they give off gases. This process is called fermentation. The fermentation causes the cow to belch and pass as much as 1000 liters of gases per day.(Howard & Wattuaux, 2003)
The food particles in the rumen are swished back and forth to the reticulum. The rumen and the reticulum share the microorganisms. After anywhere from 20 to 48 hours of circulating between the two chambers, the fermented food is passed to the omasum, where leftover water and minerals are absorbed into the cow’s bloodstream. (Howard & Wattuaux, 2003) Finally, what’s left of the food moves into the fourth chamber, the abomasum.
The abomasum is more like our stomach. It is full of hydrochloric acid and digestive enzymes. Anything left of the food that cannot be broken down by the strong acids is passed out of the cow through the intestines. The small intestine oozes digestive enzymes and absorbs nutrients and water. The large intestine absorbs even more water. By the time the food passes through the large intestine, all that is left is manure, which is dropped in the field. (Howard & Wattuaux, 2003)
To see how the digestive system on the cow produces methane gas click on the link to the animation below.
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This rubric, Cow Digestion, was created using the TaskStream Tools of Engagement.