Ruminant Digestion



This is not a very technical description of the ruminate digestive system. This page is meant to offer a quick study and promote the the desire to learn more about what should be the reason ruminates are chosen instead of other livestock.

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Rumen - The Paunch

     The rumen, often called the cows fermentation vat, is the largest part of the ruminate stomach. Feed, water and saliva are enter the rumen through the esophagus and is mixed with the rumen bacteria that latch on to the surface area and begin to eat or digest the solid the feed. The solid feed is swallowed, regurgitated, and swallowed again (Chewing The Cud). The rumen is made up of several "sacs" where the contents are moved in and out of.

     As the rumen bacteria digest the the feed they reproduce and are than passed on to other parts of the digestion system to be used a source of nutrition. They also synthesize B & K vitamins.

     As the feed is digested by the rumen bacteria some is absorbed in the rumen and the rest flows into the reticulum.

        Once in the rumen the feed is also sorted with heavy particles (large seeds, grains) sinking to the reticulum. 


     The reticulum is called the honeycomb because of the appearance of it's lining. As the smaller and more dense material is pushed into the reticulum some of the larger particles are sent back to the rumen. The small particles and some bypass feedstuff are ejected along with microbe-laden fluid into the omasum.

     The reticulum also the hardware stomach because it collects trash such as metal, some gravel ect.


Is the combination or the rumen and the reticulum. While separate sections they function as one. With feed being moved back and forth between them until it is ready to move into the omasum. Contractions originating in the reticulum move around the rumen. This process involves a wave of contraction followed by a wave of relaxation, so as parts of the rumen are contracting, other sacs are dilating. This keeps the digesta moving aiding in mixing with saliva and microbe activity.  


     Called the "manifold" stomach because it has folds similar to pages of a book where much of the water is absorbed into the cows system along with some nutrients.

Abomasum - The true stomach

     This the section of the cows stomach that is most like the stomach of non-ruminates. Here hydrochloric acid  and enzymes (pepsin which breaks down proteins) are produced. Other other digestive enzymes from the pancreas enter the abomasum to aid in breaking down fats. The acid and enzymes also help prepare microbes in the fluid to be absorbed and break down by-pass protein and nutrients in grains to be absorbed in the small intestine.

Chewing The Cud

     Suppose a cow can swallows a two inch cube of food. She eats 8 cubic inches of food with 24 sq. in. of surface area. Than the two inch cube is forced back into her mouth and she breaks this cube into 8, 1inch cubes with a total of 8 cubic inches of food with 48 inches of surface area. The amount of feed has stayed the same but the surface area has doubled. The number of rumen bacteria that can attach to the surface area and eat the food has also doubled. Every time the food is chewed the surface increases allowing for a more compete consumption of the food by the rumen bacteria. The bacteria can multiply at a greater rate providing more bacteria to pass out of the reticulum to become the main nutrition source for the cow. This "cud chewing" process increases the feed efficiency of the cow decreasing the amount of fed needed for body  maintenance or increasing the amount of weight gained per pound of feed consumed. 


Ruminants produce large quantities of saliva, estimated amounts for adult cows are in the range of 100 to 150 liters  produced per day. Aside from its normal lubricating qualities, saliva serves at least two very important functions in the ruminate stomach:: (1) Provides the fluid for the fermentation vat and (2) alkaline buffering - saliva is rich in bicarbonate, which buffers the large quantity of acid produced in the rumen and is critical for maintenance of rumen pH.

Rumen problems & care


Normal rumen pH is 6.5 to 6.8,

 Abomasum is 3.5 to 4