The question of how many stomachs a rabbit has is a common misconception. The simple answer is that a rabbit possesses only one stomach, making it a monogastric animal. This single-chambered structure is similar to that of humans and many other mammals, yet the rabbit’s entire digestive system is highly specialized. This unique anatomy and complex digestive processes allow them to thrive on a high-fiber diet that is often nutritionally poor.
The Single-Chamber Stomach
The rabbit’s stomach is a simple, single-chambered organ with thin walls, accounting for approximately 15% of the total gastrointestinal tract volume. Its primary function is to begin the digestive process through chemical breakdown and sterilization. The adult stomach maintains a highly acidic environment (pH 1 to 2), which effectively sterilizes the large volume of vegetation the rabbit constantly consumes.
A distinctive anatomical feature is the tight muscular ring at the stomach entrance known as the cardiac sphincter. This strong muscle makes it physiologically impossible for a rabbit to vomit or regurgitate its stomach contents. Because food cannot be expelled backward, the stomach contents must continually be pushed forward. This anatomical constraint means the digestive tract is built for constant, rapid movement, unlike the multi-chambered stomachs of ruminants like cows.
The Cecum: Rabbit’s Fermentation Vat
While the stomach is monogastric, the rabbit compensates for the low nutrient density of its diet through a specialized pouch in the hindgut called the cecum. This organ is proportionally the largest cecum of any mammal, sometimes comprising 40% to 60% of the total volume of the gastrointestinal tract. This size often leads people to mistakenly believe the cecum acts as a second stomach.
The cecum functions as a microbial fermentation vat, similar to the rumen in cows, but located after the stomach and small intestine. Within this chamber, beneficial bacteria and protozoa break down fibrous material that the stomach and small intestine could not digest initially. The rabbit’s digestive system employs a mechanism in the colon to separate ingested material. Long, indigestible fiber is quickly sorted and passed as hard fecal pellets, while small, fermentable fiber particles are shunted backward into the cecum for microbial digestion.
Cecotrophy: The Essential Digestive Process
The fermentation process in the cecum yields a nutrient-rich byproduct, a unique behavior called cecotrophy. This process involves the formation of cecotropes, which are specialized soft pellets distinct from the rabbit’s dry feces. These soft pellets are rich in essential nutrients, including microbial protein, amino acids, and water-soluble B vitamins, such as B12.
The cecotropes are passed and eaten by the rabbit directly from the anus, often at night or in the early morning, leading them to be mistakenly called “night feces.” They are swallowed whole, protected by a thick mucus coating added in the colon. This coating shields the beneficial bacteria and nutrients from the stomach’s highly acidic environment during the second pass. This second digestion allows the nutrients, which bypassed the small intestine initially, to be properly absorbed, making cecotrophy essential for nutritional balance.
Dietary Implications for Digestive Health
The anatomical structure and specialized processes of the rabbit’s gastrointestinal tract make its health dependent on a high-fiber diet. Indigestible fiber is the principal driving force for normal peristalsis, the muscular contractions that move food through the gut. Without sufficient coarse fiber, the system slows down, a dangerous condition known as gastrointestinal (GI) stasis.
Hay, especially long-stem grass hay like timothy or orchard grass, must form the majority of a rabbit’s diet because it provides the necessary abrasive, indigestible fiber. When a rabbit consumes a diet too low in fiber and too high in carbohydrates, gut motility decreases, and the delicate balance of the cecal microbes can be disrupted. This lack of movement leads to a slowdown of the system, causing painful gas buildup and dehydration of the contents, which can quickly become a life-threatening emergency.