Why does rumen stink?

The rumen of a cow stinks due to the process of fermentation that takes place within it. The rumen is one of the four chambers of a cow's stomach, and it is where plant matter is broken down by microorganisms. During fermentation, these microorganisms produce various gases, including methane, carbon dioxide, and hydrogen sulfide. These gases have a strong, unpleasant odor that can be detected when a cow belches or when rumen contents are released into the environment. Additionally, the rumen contains a large amount of bacteria and other microorganisms, which can also contribute to the odor.