When a deer feeds, it quickly fills its rumen. Later, it regurgitates the food and chews it more thoroughly. Rechewing helps digestion and allows microbes to break down cellulose and other plant fibers into easily digested materials. It forces water into the rumen, suspending food particles and floating them to the reticulum where the digeston continues. Similar processes occur in the rumen and reticulum, but most material in the reticulum consists of smaller particles.
Food also passes to the esophagus for rechewing.
This compartment most closely resembles the stomach of nonruminants. It secretes enzymes that further digest the products created by microbial action and the microbes themselves. Further digestion takes place in the small intestine. Generally deer from northern climates have larger body sizes and weigh more than their southern counterparts. This principle, called Bergman's Rule, holds true for most mammals and is most pronounced at the extreme northern and southern reaches of an animal's range.