Horses eat their own poop for different reasons depending on their age. In foals, it’s a normal and essential developmental behavior that seeds the gut with beneficial bacteria. In adult horses, it almost always signals a problem: too little fiber in the diet, micronutrient deficiencies, or chronic boredom from confinement.
Why Foals Eat Manure
Foals are born with a essentially sterile digestive tract. To break down plant fiber later in life, they need a thriving community of specialized microbes in their large intestine. Eating their mother’s manure is how they get those microbes. A University of Kentucky study found that foals specifically acquire fibrolytic bacteria this way, the organisms they’ll depend on to digest hay and grass once they transition from milk to solid food.
The behavior starts remarkably early. Researchers have detected it as soon as three days after birth, and by one week of age, every foal in a studied group was doing it. The peak happens around two weeks old. Foals continue eating manure from about week one through week 19, with the highest frequency in the first two months of life. After that, it tapers off naturally.
Beyond gut bacteria, there’s evidence that foals may be responding to chemical signals in their mother’s feces. One hypothesis suggests a maternal pheromone draws the foal to compounds like deoxycholic acid, a bile acid the foal may need for immune development and nervous system maturation. The behavior may also provide nutrients the foal can’t yet get from other sources. In short, for a young horse, eating manure isn’t a problem. It’s a biological necessity.
What It Means in Adult Horses
Adult horses typically avoid eating feces. When they don’t, the most common explanation is a diet that’s too low in fiber. Horses are hindgut fermenters, meaning they rely on a massive microbial ecosystem in their large intestine to extract energy from plant fiber. They have a baseline requirement for roughage, and when they don’t get enough, they look for it anywhere they can, including in manure. Eating bedding, chewing wood, and consuming feces are all behaviors seen predominantly in horses fed concentrate-heavy diets rather than fiber-rich forage.
The connection is straightforward: manure still contains undigested plant fiber. A horse that’s been fed mostly grain with limited hay may turn to feces as a crude way to increase both fiber intake and foraging time. Providing adequate hay has been shown to reduce coprophagia alongside other stress-related behaviors like crib-biting and aggression, while also increasing social bonding between horses.
Micronutrient deficiency is the other dietary trigger. When pasture grass matures past its vegetative phase, its fiber content rises while its protein and digestibility drop. Horses grazing on overly mature pasture, or those on poorly balanced diets, may eat manure in an attempt to recapture nutrients their body is missing. In adult horses, the behavior can be a visible flag that something in the diet isn’t right.
Boredom and Confinement
Horses evolved to graze 14 to 17 hours a day across open terrain. A stall-kept horse with limited turnout and restricted feeding windows has enormous amounts of unoccupied time. That idle time, combined with insufficient roughage, creates the conditions for coprophagia. The behavior is rarely seen in horses with free access to pasture or ad libitum hay. It’s overwhelmingly a problem of managed environments where feeding is restricted and movement is limited.
Parasite Risks From Eating Manure
Whether it’s a foal eating its dam’s feces or an adult horse picking through a manure pile, consuming feces carries real health risks. Horses typically pick up intestinal parasites by ingesting grass or hay contaminated with manure containing parasite eggs or larvae. Eating feces directly is an even more concentrated exposure.
The parasites of greatest concern include:
- Large strongyles (bloodworms): Among the most harmful horse parasites. Their larvae damage blood vessel linings, forming clots that can break free, block blood flow, and cause tissue death, severe colic, or inflammation of the abdominal lining.
- Small strongyles (cyathostomes): Cause weight loss and intermittent colic. Encysted larvae can remain dormant in the intestinal wall before emerging in large numbers.
- Ascarids (roundworms): Primarily affect horses under one year old. These six- to twelve-inch worms can number in the hundreds in the small intestine, causing poor growth, coughing, diarrhea, intestinal blockages, and sometimes death.
- Tapeworms: Attach at the junction of the small and large intestine, causing colic. Heavy infections can lead to weight loss or intestinal rupture.
- Pinworms: Less dangerous but cause intense itching around the tail and anus.
For foals, the developmental benefits of coprophagia appear to outweigh the parasite risk under normal conditions, but it underscores why a solid deworming program matters from an early age. For adult horses, the parasite exposure is all downside.
How to Stop the Behavior in Adults
Because the root cause is almost always dietary or environmental, the fix targets those areas directly. The single most effective change is increasing forage. Horses should have access to enough hay or pasture to meet their fiber requirements, ideally spending a large portion of their day chewing. For horses in stalls, slow-feeders or hay nets can extend the time it takes to consume a meal, mimicking natural grazing patterns and reducing idle hours.
Evaluating the overall diet for protein, mineral, and vitamin balance is the next step. Horses on mature pasture or limited hay may need supplementation to close nutritional gaps. If the behavior persists despite adequate forage, a micronutrient deficiency is worth investigating.
Increasing turnout time, providing social contact with other horses, and adding variety to the environment all reduce the boredom component. Horses that can move freely, interact with herd mates, and forage throughout the day rarely eat manure. The behavior is a signal that something fundamental about the horse’s care needs to change, and in most cases, the solution is more fiber, more time outside, or both.