How a cow chows

Science World, Jan 21, 2002

Ruminants (such as cows, sheep, goats, giraffes, moose, antelope, caribou, and deer) grow robust even though they eat hay and grass--foods they can't digest without a little help. A cow would die of starvation if it weren't for the billions of microbes that live in its gut and feed on plant matter, turning it into digestible nutrients. Study the diagram below to learn amazing features of the ruminant digestive system:

RUMEN A cow can pack away more than 160 liters (40 gallons) of food and water in its rumen, or first stomach chamber! Billions of fungi, bacteria, and protozoa live here. They thrive anaerobically (without oxygen) and produce enzymes (proteins) that break down plant matter like cellulose and fiber. In the process, the microbes produce methane gas (which the cow releases by belching) and vital nutrients (which the cow absorbs).

SMALL INTESTINE Muscles in the intestine move food down the tract, while fingerlike villi on the small-intestine wall secrete enzymes to aid digestion and absorb nutrients.

OMASUM The third stomach has many layers for absorbing nutrients.

ESOPHAGUS Muscle contractions move food down to the rumen--and then move undigested food (cud) back up to mouth for rechewing.

RETICULUM The second stomach chamber is far smaller than the rumen. The reticulum helps move cud up the esophagus for rechewing.

ABOMASUM The fourth stomach is a true stomach, and it works basically the same way your stomach does. The abomasum secretes enzymes and acid that break down proteins.

[ILLUSTRATION OMITTED]

Use the diagram and the article "Does My Gas Cause Global Warming?" (p. 18) to help you answer the questions below. Write answers in complete sentences.

1. How many stomachs does a cow have? What is the name of the largest stomach? How much food and water can it hold?

2. Why does a cow need its rumen?

3. What is cud? What is its purpose?

4. Why do cows belch? Why are cow belches a problem for Earth's climate? What can be done to remedy the problem?

5. Which stomach of a cow is similar to your stomach?

ANSWERS

1. A cow has four stomachs. The largest is the rumen, which holds more than 160 liters of food and water.

2. On its own a cow can't digest the hay and grass it eats. The rumen contains billions of microbes that break down plant cellulose and fiber into nutrients that a cow can actually use.

3. Cud are wads of undigested food that a cow regurgitates from its rumen and ruminates.

4. Cows belch because the microbes in the rumen produce gas. This gas contains methane, a greenhouse gas. Dietary supplements and vaccination can help reduce the amount of methane in belches.

5. The abomasum, the cow's fourth stomach, functions much like the human stomach.