igestion is the breakdown of food into smaller components that we can absorb and use for energy. The gastrointestinal tract varies greatly between animals and is mostly developed by what they consume. Humans, for example, have a monogastric stomach that secretes hydrochloric acid that breaks down food, but also lacks enzymes that are able to digest cellulose.
Forage consuming species, such as cows, rely on grass as their main form of food and have a ruminant digestive tract that allows the breakdown of otherwise indigestible cellulose in plants thanks to enzymes and protozoa. Other than a specialized multi-compartmental stomach, there is very little difference between a monogastric and ruminant gastrointestinal tract. In order of passage: