The rumen is the first stomach compartment in cattle, where swallowed food is initially collected.
Cattle are ruminants, meaning they digest plant material with help from microorganisms and later regurgitate partially digested food as cud. The rumen is the largest compartment and acts as a fermentation chamber rather than functioning like a simple human stomach.
Bacteria, protozoa, and fungi in the rumen break down cellulose from grasses and other fibrous plants. Their activity produces volatile fatty acids, which supply much of the cow’s usable energy.
The rumen is followed by the reticulum, omasum, and abomasum. The abomasum is the compartment most similar to a conventional glandular stomach, so it is sometimes called the “true stomach.”