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Explain the process of digestion in ruminants why do ruminants digest their food in two steps.

 They are unable to digest plant material directly, because they lack enzymes to break down cellulose in the cell walls. Digestion in ruminants occurs sequentially in a four-chambered stomach. Plant material is initially taken into the Rumen, where it is processed mechanically and exposed to bacteria than can break down cellulose (foregut fermentation). The Reticulum allows the animal to regurgitate & reprocess particulate matter ("chew its cud"). More finely-divided food is then passed to the Omasum, for further mechanical processing. The mass is finally passed to the true stomach, the Abomassum, where the digestive enzyme lysozyme breaks down the bacteria so as to release nutrients. Use of plant material is thus indirect, with primary processing by the bacterial flora maintained in the stomach.


Most animals that have a basic stomach with one compartment, cattle have a more complex stomach separated into four distinct chambers.  Animals that have a stomach with compartments capable of digesting the high amount of cellulose found in very fibrous forage are known as ruminants.  The term ruminant is related to the second chewing of large pieces of forage that return to the mouth from the stomach – known as chewing the cud.  While most animals secret acids and enzymes into the stomach for digestion, ruminants use a very unique fermentation process to break down food into useful nutrients.


    Reticulum
    Rumen
    Omasum
    Abomasum

These four compartments work in a coordinated way to break down highly fibrous forage in order to release the sugars and proteins contained in the plant’s densely walled cells.

The reticulum and the rumen, the first two chambers, are very connected and are continually exchanging contents, to the degree that they are commonly referred to together as the reticulo-rumen.  The rumen, which is by far the largest stomach section in mature cattle, is where the fermentation takes place, and where an important mixture of bacteria, fungi, and other micro-organisms aid the slow, two to four days fermentation process.  The contents of the reticulum continually mix with the contents in the rumen.  In the reticulum, the contents are sorted with the largest pieces returned to the mouth for additional chewing and the smallest pieces sent to the next chamber, the omasum, for the next stage of digestion.  The rest remain in the rumen for further fermentation.

The omasum contains many folds that effectively absorb liquids, which it passes on to the blood stream.  The last compartment, the abomasum, is similar to the stomachs found in most animals.  It uses acids and enzymes to further break down the particles so that they can be absorbed into the blood stream.  It also breaks down proteins and other by-products of the fermentation process.


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