Ruminant animals are hoofed herbivorous mammals that have a unique digestive system that allows them to better use energy from fibrous plant material than other herbivores. They 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 takes place in the front part of the digestive system and therefore is called foregut fermentation, typically requires the fermented ingesta (known as cud) to be regurgitated and chewed again. Ruminants have a four-chambered stomach that includes the rumen, reticulum, omasum, and abomasum. The rumen microbes ferment feed and produce volatile fatty acids, which is the main energy source for the animal. Ruminants include both domestic and wild species, such as cattle, all domesticated and wild bovines, goats, sheep, giraffes, deer, gazelles, and antelopes. They are also the only mammals capable of digesting food without fully chewing it.