Question: We have a yearling colt that has not yet been gelded. He seems to be depositing manure in certain spots along the fence row. What is going on?

Answer: Your colt is displaying elimination marking behavior, a very common occurrence in stallions. The behavior is normally exhibited in response to the urine or feces of other horses, particularly mares. The stallion will perform a highly stylized behavior sequence, including sniffing the ground (or piles of feces or spots of urine); performing the Flehman response; dropping his penis and urinating on the spot of interest; defecating on the spot; sniffing and circling of the pile and ground nearby. Manure tends to build up in these areas, creating what is known as stud piles. These stud piles often form along fence rows where stallions are pastured. The behavior is sometimes called a play behavior in foals and immature yearlings.

Mares do not normally perform elimination marking behavior, and performance of such a behavior may indicate higher than normal levels of androgens or estrogens. In general, stallions keep the cleanest stalls and paddocks (defecating in certain spots only), geldings keep the next cleanest (perhaps from performing play elimination marking behavior as foals), and mares generally have the messiest stall, indicating no preference for specific area of defecation. Of course this can differ from horse to horse.

Elimination marking behavior is not an abnormal behavior in colts, and is observed by domesticated and feral stallions, including both harem and bachelor stallions. Even after gelding, the colt may continue to display the behavior, particularly if kept in the same paddock. However, the behavior may completely disappear as his hormone levels decrease after gelding.