Ruminant

Ruminant is a term used to describe mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. The process, which typically requires the fermented ingesta (known as cud) to be regurgitated and chewed again, is called rumination. The word "ruminant" comes from the Latin ruminare, which means "to chew over again".

Anatomy and physiology

Ruminants have a unique digestive system that allows them to better use energy from fibrous plant material than other herbivores. Unlike monogastrics such as swine and poultry, ruminants have a four-compartment stomach. The four parts are the rumen, the reticulum, the omasum, and the abomasum. In the first two chambers, the rumen and the reticulum, the food is mixed with saliva and separates into layers of solid and liquid material. Solids clump together to form the cud (or bolus). The cud is then regurgitated and chewed to completely mix it with saliva and to break down the particle size.

Classification

Ruminants are classified into three different suborders: Sciuromorpha, Hystricomorpha, and Castorimorpha. The Sciuromorpha includes the most diverse group of ruminants, including deer, cattle, goats, and sheep. The Hystricomorpha includes a number of ground-dwelling species, such as porcupines and guinea pigs. The Castorimorpha, a group that includes beavers and kangaroo rats, are the only ruminants that do not have a complex stomach.

Evolution

The evolution of ruminants is characterized by a steady increase in body size, a trend that is also observed in many other mammalian clades. The earliest ruminants date back to about 50 million years ago, and the ruminant family tree is divided into two main branches: the Cervidae (deer and their relatives) and the Bovidae (cattle, goats, sheep and their relatives).

See also

• Digestion
• Herbivore
• Foregut fermentation

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