The reticulo rumen
The reticulorumen is composed of the rumen and the reticulum. The reticulorumen is partially separated from the rumen by the reticular fold, which allows mixing between the two compartments. The contents of the reticulorumen are mixed by contractions of the reticulorumen wall. The mixing recirculates undigested material preventing the rumen becoming clogged and distributing symbiotic bacteria throughout the ingested material. The reticulorumen becomes colonized by symbiotic bacteria in the first week after birth. The bacteria help to break down the food and release nutrients by a fermentation
When food has been broken down enough, it passes from the reticulorumen through the reticulo-omasal orifice. The omasum wall is highly folded, giving a large surface area which allows for the efficient absorption of water and salts released from the partially digested food. The omasum also acts as a type of pump, moving the food from the reticulorumen to the true stomach, the abomasum, where acid digestion takes place.
Unlike a ruminant's three forestomachs, the abomasum is a 'secretory stomach'. This means that cells in the abomasum wall produce enzymes and hydrochloric acid which hydrolyse proteins in the food and also in the microbes mixed in with the food. Hydrolysis breaks the proteins into smaller sub-units (eg dipeptides and amino acids), ready for further digestion and absorption in the small intestine. Because ruminants eat such large amounts of plant material, there is an almost continuous flow of food through the abomasum. In comparison, activity in the stomach of monogastric animals generally has a circadian rhythm associated with food intake (Djikstra, 2005)