A cow has four stomachs. There are different processes that the digestive process of the cow has to go through to ensure that it will be able to eat and digest everything. The first process is when the cow eats food and decides to swallow the food.
The moment that the food is swallowed, that is the time when digestion may start. Take note that while the cow may chew the food, it will just chew the food enough so that it can be swallowed. The other two stomachs will digest the partially chewed food. The last stomach will store the food until such time when it would be needed by the body of the cow.