Rabbits are popular pets. It’s important for rabbit owners to understand the ways that the rabbit digestive system is very different from that of most other companion animals. Rabbits are "hind-gut fermenters." Their digestion more closely resembles that of a horse than the digestive systems of dogs or cats.
Like dogs and cats (and humans) rabbits ingest food through their mouths, where it is chewed, ground into small pieces and mixed with saliva. In the stomach, the food is mixed with acid and enzymes to start digestion. Most nutrients are absorbed in the small intestines and are passed through the intestinal lining into the blood stream. However, enzymes can’t break down fiber, so that part of the food continues to the colon to be sorted into digestible and undigestible components. The undigestible fiber is excreted as feces.
The small particles of digestible fiber are diverted to the caecum where bacteria ferment it so that the fiber breaks down into digestible components. These small bits of digestible fiber are coated in mucus and then excreted as cecotropes. Cecotropes are special droppings which the rabbits eat, often as they exit the anus, in order to get the additional nutrients from fiber. Unlike rabbits' feces, which are usually dry pellets, the cecotropes look like soft, shiny pellets and often have a strong order.
The healthiest diets for rabbits include lots of high quality, digestible grasses and some fresh vegetables, especially leafy greens. Of course, the exact ingredients and quantities should be calculated to meet your pet’s individual needs. A great resource for companion rabbit owners is the House Rabbit Society at https://rabbit.org .