A plant-eating animal that brings back swallowed food into the mouth to chew it again is called a ruminant and the process is called rumination.
Ingestion: Ingestion The food is ingested with the help of the tongue and chewed. Ruminants have sharp incisors and large molars to bite and chew grass. They also have powerful jaw muscles.
Digestion: After being chewed once, the food passes down the 2 to 3 feet long oesophagus. The oesophagus leads into the stomach. The stomach of ruminants has four chambers: rumen, reticulum, omasum, and abomasum.
(A cow makes 40,000 to 60,000 jaw movements per day).
Rumen: The rumen helps in storing the large quantities of food that has been quickly consumed. The food is partially digested here and is now called the cud. The cud is then brought back to the mouth, re-chewed, and re-swallowed in a process called cud-chewing. The rumen has billions of bacteria and protozoa, which break down the carbohydrate calls cellulose found in hay and grass.
Reticulum: The reticulum helps in moving the swallowed food back into the mouth for thorough chewing. The reticulum opens into the omasum.
Omasum: The omasum absorbs excess water.
Abomasum: The walls of the abomasum secrete digestive juices.
Absorption: Absorption begins in the four-chambered stomach, but the main absorptive organs are the Intestines.
The food from the abomasum passes into the small intestine, where it mixes with secretions from the pancreas and liver. Most of the digestion of carbohydrates, proteins, and fats takes place here. Several villi are present here, which help in increasing to surface area for absorption.
The small intestine leads into the large intestine. The main function of the large intestine is to absorb water and eliminate the undigested food as faeces.
In a cow, the process of digestion takes 70-100 hours, as compared with 2-24 hours in humans. This however, permits them to obtain as much nutrition as possible from the plant materials.