• Question: Why does a cow have 4 stomachs

    Asked by paulfee1 to Cathal, Ciara, Emma, Michael, Sive on 14 Nov 2013.
    • Photo: Michael Nolan

      Michael Nolan answered on 14 Nov 2013:

      Hi PAul,

      Cows have 1 stomach, but it has 4 compartments, so maybe this is one of those ideas that has propogated through the years, in particular as it sounds a bit crazy!
      The compartments are called the rumen, reticulum, omasum, and abomasum.
      The rumen is the site of fermentation of the cow’s feed, the reticulum is where dense food and non-food objects are collected (we eat it in Cork as Tripe), the omasum is used to soak up certain nutrients from the food into the body and the abomasum is where rennet is secreted (used to make cheese).
      Cows are ruminants so they can eat usually undigestible food by “chewing the cud” . The 4 compartments probably developed to handle digestion of such food, where one stomach compartment, such as in humans, was not enough.

      hope this helps

      M

    • Photo: Sive Finlay

      Sive Finlay answered on 14 Nov 2013:

      Hi Paul
      Thanks for the question and cool answer from Michael. I’d just add that the main reason cows need their four “stomachs” (really different chambers) is because grass is not a very nutritious food. Grass (and the other types of plants that also grow in pasture land) is a good source of carbohydrate and some protein but it also contains lots of cellulose, lignin and even silica which are difficult to digest (silica also wears down teeth so when grasslands started spreading across North America around 15 million years ago that created a selective pressure for horses to evolve longer teeth to deal with all the wearing down from silica). Cows need their specialised chambers to deal with their tough food source and to try to extract as much nutrition from the plant as possible.
      Other herbivores deal with their tough food in different ways to ruminants. Herbivores tend to have long large and small intestines so they can absorb nutrients from their food and some animals such as rabbits and horses are hindgut fermenters which means they have specialised bacteria in their large intestines to break down their plant food.
      Sive

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