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The ruminant digestive system

Quick facts

  • Ruminant stomachs have four compartments: the rumen, the reticulum, the omasum and the abomasum.

  • Rumen microbes ferment feed and produce volatile fatty acids, which is the cow’s main energy source. Rumen microbes also produce B vitamins, vitamin K and amino acids.

  • In calves, the esophageal grooves allows milk to bypass the rumen and directly enter the abomasum. Rumen development occurs following a change in diet and microbial growth.

The digestive tract of the adult cow

The cow’s digestive tract
The cow’s digestive tract

The cow's digestive tract consists of the following.

  • Mouth
  • Esophagus
  • A four-compartment stomach, which includes
    • The rumen (paunch)
    • The reticulum (“honeycomb”)
    • The omasum (“manyplies”)
    • The abomasum (“true stomach”)
  • Small intestine
  • Large intestine
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Digestive tract functions

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Calf digestive system

The rumen, reticulum and omasum remain undeveloped at birth and during the first few weeks of life. The calf’s largest stomach compartment is the abomasum. At this stage of life, the rumen doesn’t function and thus some feeds that mature cows can digest, calves can not. 

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James Linn, former Extension animal scientist -dairy nutrition; Michael Hutjens, Emeritus professor, University of Illinois; Randy Shaver, professor, University of Wisconsin; Donald Otterby, former professor, College of Food, Agriculture and Natural Resource Sciences;  W. Terry Howard, former Extension Dairy Specialist, University of Wisconsin and Lee Kilmer, Emeritus professor, Iowa State University

Reviewed in 2018

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