It is a very popular but incorrect thought that a cow has 4 stomachs. To be precise a cow does not actually have four stomachs but in fact has one stomach but that has four stomach chambers. Each chamber has a different but an important part to play in digesting food. The grass a cow eats has a long and complicated process from the eating stage to finally being passed back out the other end!
The four chambers of the cows stomach are the rumen, the reticululum, the omasum and the abomasum. The grass or digested material passes through each of these four chambers in turn and is slowly digested and the goodness drawn out. Each chamber works in the following ways -
1. The Rumen - This is the largest chamber and can hold up to 150-200 litres of partly digested food. The Rumen is full of good bacteria and this softens and helps digest the food. The bacteria ferments the carbohydrates in the food to allow the cow to produce energy. In doing so gas is produced (approx 500-1500 litres a day), approx 30% of this is methane gas and is expelled during belching. This is also how the foodstuff is passed from one chamber to the next.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />
2. The Reticululum - This softens the food even further and forms it into small lumps of cud. The cud is returned to the cows mouth and chewed approx 40-60 times before being swallowed again. The reticulum also prevents large items from passing through the stomach this includes items which the cow has eaten which are not food, e.g plastic, packaging etc. Its like a safety mechanism for the cow. The material sits here and will not pass through to the next chamber, eventually the items will build up and the cow will vomit it back up.
3. The Omasum - This processes the cud further by pressing and breaking it up. It is then filtered. The omasum also regulates fluid absorbtion in the gut.
4. The Abomasum - This works similar to the human stomach. The food is finally digested by the stomach juices and the useful nutrients are absorbed by the blood. The waste is then pushed out into the intestines and finally out into a big smelly cow pat! Its a long journey for a bit of grass!
So next time you see a cow eating some grass in a field, bear in mind the work its stomach has to do just to digest that one mouthful of grass! Its not quite as simple as us having a quick munch of a snack.