The rumen is a fermentation vat par excellance , providing an anaerobic environment, constant temperature and pH, and good mixing. Well-masticated substrates are delivered through the esophagus on a regular schedule, and fermentation products are either absorbed in the rumen itself or flow out for further digestion and absorption downstream. Ruminants evolved to consume and subsist on roughage - grasses and shrubs built predominantly of cellulose. Dynamics of Cranial Digestion Feed, water and saliva are delivered to the reticulorumen through the esophageal orifice. Added to this mixture are voluminous quantities of gas produced during fermentation.
Ruminants produce prodigious quantities of saliva.
The rate of flow of solid material through the rumen is quite slow and dependent on its size and density. Water flows through the rumen rapidly and appears to be critical in flushing particulate matter downstream. As fermentation proceeds, feedstuffs are reduced to smaller and smaller sizes and microbes constantly proliferate. Ruminal contractions constantly flush lighter solids back into the rumen. The function of the omasum is rather poorly understood.