Written by Laura Atkins and Susan Smith Ph.D.

Rabbits have a unique digestive system that is very good at taking energy (calories) and nutrients from food that is low in both. The cecum, a specialized organ located at the junction of the small and large intestines, contain a mix of bacteria that enable the rabbit to survive on low calorie, high fiber foods. This also means that if a rabbit fed a diet too low in fiber is at risk for stomach (gastrointestinal) disorders.

Digestion begins in the mouth, where food is mashed up by the teeth and mixed with saliva. Enzymes in the saliva begin the process of breaking down food into pieces small enough to move into the blood. When food is broken up and moist, the bunny swallows and the food enters the stomach. In the stomach the food is mixed with stomach acid and different enzymes continue the process of digestion.

Once food has been broken into even smaller pieces by the stomach, it moves into the small intestine. Small water-soluble nutrients such as sugars, amino and nucleic acids, and non water soluble fats are absorbed in this region. Larger indigestible molecules such as fiber are passed into the large intestine. Once in the large intestine the material is sorted by size. Smaller fragments are moved backwards into the cecum for use by the cecal bacteria. Larger fiber fragments are passed to the large intestine and then excreted as fecal pellets.

The rabbit cecum contains a complex mix of bacteria that break down, or "ferment" the fiber the rabbit cannot digest. The bacteria use the energy generated during fermentation to grow. Byproducts of fermentation include vitamins, volatile fatty acids (VFA's) and essential amino acids, all of which can be used by the rabbit. Volatile fatty acids are absorbed directly into the bloodstream through the lining of the cecum and provide approximately 30% of the energy required by the animal. Nutrients that cannot be absorbed directly into the bloodstream pass through the large intestine and are excreted as "cecal pellets" Cecal pellets are different from the round bunny droppings that are left in the litterbox, they are soft, grapelike clusters that have a distinctive smell.

Rabbits consume cecal pellets directly from the anus, called "coporphagy." While this may sound distasteful to humans, it is essential to a rabbit's health. Rabbits receiving a high fiber diet consume all of their cecal pellets, so you may have never seen any. Rabbit diets that are too rich in protein, too high in energy and too low in fiber may cause more cecals to be produced than the rabbit can or desires to eat. In this case, the excess cecal pellets may become smeared all over bunny, his cage, or your carpet. They may also form a hard lump at the base of the rabbit's tail.

One important thing to remember about the rabbit digestive system is that most diseases of the rabbit eventually end up disrupting normal digestion. Because different diseases and different treatments affect the balance of bacteria in the cecum, sick rabbits may not be receiving the benefits from the cecal bacteria. Therefore, foods that are adequate to meet the nutritional needs of a healthy rabbit may not be adequate for a sick rabbit.

Carbohydrates Fiber Protein Fats
Vitamins Minerals Nutrient Requirements

Overview of Digestion

Written by Laura Atkins and Susan Smith Ph.D.