The ruminants such as cow eat grass and all which have cellulose in it.but cellulose cant be chewed and digested fast.that is why they swallow it and it goes to caecum an organ which  only ruminant animals have.there it is digested and is made into cud which comes back when the cow is free and it  chews it proparly cause they have no digestive system like other animals.
1 1 1
Cows and buffaloes swallow food hurriedly so that they can store maximum food in their Rumen. Rumen stores the food and keeps for some time.This helps in the process rumination by pushing the food back into the mouth so that the cattle can chew it properly and make it easy for digestion as the saliva breaks it into simpler substances and then it is swallowed back to the rumen for digestion.