Ever Wondered How a Cow's 4 Stomachs Work? Rumen: The rumen ferments and breaks down tough plant fibres into simpler substances with the help of billions of microbes. Reticulum: The partially digested food forms into smaller particles called cud, which the cow regurgitates and chews again to further break it down. Omasum: The omasum acts like a filter, absorbing water and minerals from the cud before passing it along. Abomasum: The cud reaches the abomasum, which is similar to a human stomach. H