A: I don’t know exactly why your two geldings are different. But defecation habits are so interesting! Here’s a little background: Horses grazing at will tend to defecate and move on. Domestic horses at pasture tend to have latrine areas where there’s a concentration of manure piles. Since horses tend to avoid grazing near manure piles, this area is usually undergrazed, despite often having some pretty nice grass due to the nutrients from the manure.
Stallions have an elimination-marking sequence when they encounter a manure pile from another horse, which includes a ritualized sequence that goes something like this: sniff, or maybe paw at it, show a flehmen response, defecate or urinate on or near the pile, maybe sniff it again, and move on.
You will also commonly see “stud piles” of manure. A singly housed stallion will make these piles of manure, and they will also be formed by multiple stallions defecating over each others’ manure. You’ll see these stud piles along fence lines, at gates, and in open areas where there are common stallion or harem group crossings. I saw stud piles near an asphalt road in a Mustang-populated area outside Reno, Nevada, and learned that was a favored crossing for the local bands and harem groups. Defecation might also occur amidst agonistic encounters between stallions.
So considering these natural behaviors, perhaps these two geldings are interacting with their environment and with each other or with other horses in adjacent stalls in a way mimicking completely normal, at-will behavior. It might not be that one gelding is so messy, but that the other is particularly tidy and actually making stud piles. Although this is not a common behavior in geldings, some stallionlike behavior is often retained beyond castration.
If you have the chance to watch the messier gelding for long periods of time, or put him on video surveillance. It would be interesting to know what his movements about the stall are like. Is he nervous or uneasy appearing, or slowly moving about the stall nibbling on hay as if grazing? As we’ve all seen, horses that get excited or nervous tend to defecate and often this appears soft and with poorly digested feed, suggesting some change in overall gut motility.
Or manure might start in the same location then just gets trounced around. If your messy gelding appears to be so because of nervousness or restlessness, you might think about any management changes that could reduce his nervousness in the stall. This is not to fix the messiness problem per se, but to improve his overall well-being. For example, consider more turnout time, more hay, a change in his ability to see other horses, or rearranging neighbors. On the other hand, moving about the stall in a slow deliberate fashion might be a good thing, as the horse is just reproducing normal outdoor grazing and defecation behavior.
Other than creating a dirtier stall for the caretaker and probably some manure stains that need to be groomed out, there aren’t necessarily any health hazards for the messy gelding. If the stall is cleaned well on a daily or more frequent basis, the flooring is slip-resistant, and the barn is well ventilated, I don’t think this horse should have medical problems more so than the other. However, another thing to consider is whether the messiness is due to either a primary digestive disturbance or increased water intake and urination. So if this is something new for this gelding and there have been no other changes in his housing, exercise, or social structure, then I would monitor the water intake and quality of manure output and consider having a good veterinary examination.