What is considered the true stomach of ruminants?

The abomasum is considered the true stomach of ruminants because it functions similarly to the stomach of monogastric animals, where the digestive process primarily involves the secretion of gastric juices, including enzymes and hydrochloric acid. This is the site where protein digestion occurs through the action of these digestive enzymes and acids, breaking down complex proteins into simpler amino acids for absorption in the intestines.

In contrast, the other compartments of the ruminant stomach—the rumen, reticulum, and omasum—perform different functions. The rumen is primarily involved in fermentation and microbial digestion of fibrous plant material. The reticulum allows for the mixing of ingested food and aids in the regurgitation of cud (a key component of ruminating), while the omasum absorbs water and some nutrients. These compartments work together in the overall digestion process, but only the abomasum is directly responsible for enzymatic digestion similar to that of non-ruminant stomachs. Thus, referring to the abomasum as the true stomach highlights its critical role in the digestive system of ruminants.