A bovine can eat up to 50 kilos of food per day. In the summer this mainly consists of fresh grass but often hay is also added.
Cows are ruminants and as such have a stomach with 4 chambers or “pouches”. When they graze or eat hay they swallow almost without chewing and the food accumulates in the rumen, the first stomach, where with the aid of bacteria it is partly digested. This process requires that a cow drink up to 100 liters of water per day.
At this point the process gets somewhat gross and anyone eating a tasty snack right now may want to skip this passage. While restiing, the cow now regurgitates the food and water mix into its mouth (much like a person after his 11th grappa) where it gets re-chewed, re-swallowed and deposited in the reticulum. During the various stages of mastication a cow can produce up to 200 liters of saliva a day. This process of swallowing, un-swallowing, re-chewing and re-swallowing is called rumination or more commonly “chewing the cud”.
There is little separation between the first two sections of a cow’s stomach, the reticulum and the rumen, so food and water can pass back and forth easily. The reticulum is made of muscle and by contracting it forces food into the cow’s esophagus which carries the food back to the mouth.
The next pouch in the stomach is the omasum. This pouch acts like a giant filter to keep plant particles inside the rumen while allowing water to pass freely.
After the grass pieces and other feed are broken down to a small enough size they eventually pass on to their final destination, the abomasum or “true stomach” which produces acids, buffers and enzymes to break down the food. After passing through the abomasum the partially digested food enters the small intestine where digestion continues and nutrients are absorbed and then on to the large intestine where waste in formed and then eliminated.