The act of consuming feces, known scientifically as coprophagy, appears unusual to humans but represents a necessary and sophisticated biological strategy for many animal species. This adaptation enables certain animals, particularly those consuming high-fiber plant material, to maximize the nutritional value of their diet. By cycling waste through the digestive system a second time, animals recover otherwise lost nutrients and essential microorganisms.
Why Coprophagy Is Essential for Nutrient Recovery
Many herbivorous animals rely on gut microbes to break down tough plant fibers like cellulose through fermentation. Unlike ruminants, which ferment food in the foregut, many smaller herbivores are hindgut fermenters. This means fermentation occurs in the cecum or large intestine, located after the small intestine where most nutrients are absorbed.
The beneficial microbes synthesize vitamins, proteins, and short-chain fatty acids. However, these products are produced too far down the digestive tract to be fully absorbed before excretion. Consequently, the first fecal pass contains valuable nutrition that the animal’s body could not capture. The subsequent consumption of these nutrient-rich pellets allows the material to pass through the small intestine a second time for absorption.
This biological recycling is particularly important for acquiring B vitamins, such as B12, and vitamin K, which are synthesized by the gut flora. It also allows for the recovery of microbial protein and essential amino acids. Coprophagy is a highly efficient mechanism to extract the maximum possible benefit from a low-quality, high-fiber diet.
Cecotrophy: The Specialized Digestive Strategy
The most specialized form of self-coprophagy is cecotrophy, observed in lagomorphs, including rabbits and pikas, and certain rodents like guinea pigs. These animals produce two distinct types of fecal pellets: hard, dry waste pellets and the cecotrope, often called “soft feces.” The cecotrope is formed from the contents of the cecum, where microbial fermentation takes place.
Cecotropes are soft, clustered, and covered in a protective layer of mucus. This mucus layer protects the pellet’s contents from the acidic environment of the stomach when swallowed whole. The animal typically consumes the cecotrope directly from the anus at specific times, such as early morning or late evening. Once re-ingested, the cecotrope travels to the small intestine, where the body absorbs the microbial protein and vitamins.
Cecotrophy is not an optional supplement; it is an integrated part of the digestive physiology for these species. Its absence quickly leads to malnutrition.
Other Instances of Self-Coprophagy
While cecotrophy is specialized, other instances of self-coprophagy exist in small rodents like mice and hamsters. For these species, consuming feces serves a nutritional role, helping to recover B vitamins and maintain a stable gut flora. The behavior may also be driven by environmental factors, such as the need to keep a nest clean and free of waste.
In domestic dogs, coprophagy is often a behavioral issue rather than a nutritional necessity, though deficiency cannot always be ruled out. Adult dogs may engage in this behavior due to stress, boredom, or learned behavior, such as imitating a mother dog cleaning her pups.
In the wild, young animals, including elephant and hippopotamus calves, often consume adult feces for a different reason: inoculation. This practice introduces necessary beneficial bacteria to their sterile guts. By doing so, they acquire the robust microbial community needed to transition to a plant-based diet.