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Carbohydrate digestion starts in the thanks to secreted by the . However, it happens mainly in the where, thanks to the pancreatic , starches are glycogen are digested. Cellulose on the other hand, is digested by microorganisms through a process called , which happens in a special compartment that can change depending on the species. For example, in ruminants, this process occurs mainly in the and in horses, it occurs in the and the .