Right now, I have 10 horses here. A cross section of horses acquired from several different types of farms… 7 of them are tidy, 1 of them is beyond tidy and 2 of them are very untidy.
What makes a tidy horse?
I have my theories.
THEORIES ABOUT TIDY HORSES.
My first theory is that Mama teaches the babies. If you have a tidy Mama, then the babies are tidy. For example, Mama Tess was VERY tidy. I don’t know if her dam taught her?… but MT was a show horse for many years – and even through all of those stalls and travels, she was always neat.
Having Tess in the barn for 3 years was never an issue because she did her business is the exact same, very convenient places, every day.
I believe that she taught all of her babies to be tidy. Both Wrigley and Gwen are MT’s babies and they both make sure to be clean around where they eat.

Here are half siblings, Wrigley (front) and Gwen. Both are MT’s foals. Wrigley is 11 and he is very clean. Gwen is 24 and also very fussy about her pen. The areas around their food is always clean.
–I don’t think they know that they are siblings. Gwen might, but I doubt Wrigley knows, unless Tess or Gwen told him.
My second theory is that some horses like to be clean (like people). I think if they have the space, theses of type horses would prefer to be tidy. For example, Finn and BG.
(Now, I may be also proving my first theory here as well…) Finn and BG are full siblings. They were both raised by the same dam on the same farm. They had lots of space as babies and I think their Mama taught them well… but I’m not sure because I wasn’t there. Or, this genetic line has a propensity for clean. (My Sicilian family would vouch for this trait in their line…)
All I do know is that both Finn and BG are very clean and fussy horses. They have 2 bathrooms in their pen and you will never see errant issues anywhere.
My third theory if they were not raised in a stall or small quarters, they are more discerning. For example, here we have Annie, Missy Miss and Mo. All three were wild and had access to ample space. They have never been in a small space or stalled. As you can see, their eating area is pristine.

Missy Miss and Mo. You can see their potty place, but it is far away from their food – this angle doesn’t really show the depth. You can see that their eating and drinking row is wide and clean.
My fourth theory is that some horses are OCD – just like some of us. Here we have Dalton. He is MR. CLEAN (other than playing in his water all day). Dalton was born on the range. Then he was crammed into a paddock, then he was set free again at Sweetbeau Horses. Now, he is here. Dalton has one bathroom and he is exacting, as you can see. This guy has a virtual oasis of clean in his paddock.

Dalton is OCD. His paddock is in perfect order at all times (except for the overturned feeder and him playing in his water all day).
My fifth theory is that if they were raised in small quarters in unkempt environments, they never learn to be tidy.
Case in point, my two little piggies (and pigs are clean so I’m not sure about that phrase…) but my two n’er do cleaning equines are Dodger and Norma.
They poop where they are standing. That’s it. Norma is worse than Dodger. …At least I’ve seen Dodger walk off to do his business. But not Norma.
OK, so… what do we know about these two…? Well, Dodger was a failed ‘pony ride’ pony. He was kept in a small stall and only brought out to go around in circles. (He hates kids.) I purchased him at a meat auction for $27.50 (his meat weight).
Norma was raised on a donkey farm in Oregon. I think her owner loved all the donkeys, but he was way past his prime and could not keep up with the work. The place was a mess and all the donkeys were holed up in a huge, metal building with sliding doors. In his defense, I answered his ad in the paper, asking for anyone to help him adopt out his donkeys before he died. I answered the ad. He was very sweet, knew all the donkeys by name and was kind and eager for me to adopt one. I should have gotten two. But, that was 24 years ago and I didn’t know then what I know now about donkeys.
Anyway, I think these two are messy because that was how they were raised.

Dodger and Norma. Both were raised in cramped and squalid conditions. I adopted Norma when she was 2 – and this about her has never changed. She poops where she is standing. As for Dodger, he was a prisoner of a nasty ‘pony ride’ traveling Fair person. He has scars on his back from the ill fitting saddle. Dodger was kept in very small quarters until I purchased him at a meat auction. That was 24 years ago. He has never been tidy… but then again, he has also lived with Norma that entire time (I got them at the same time), so maybe they feed off of each other’s negligence. But, they’ve had plenty of space for many years – yet they still are not tidy – at all.
Do any of you have theories?!

My first horse, Gabriel, had been a school horse (before that, a camp horse, who was put on the killer truck at the end of the season, off which the wise old horseman where I took lessons bought him; before that, no one knows, except that he was wonderfully trained) living in a straight stall when he was not being ridden. When I bought him and upgraded him to a boarder’s box stall, it took a little while for him to get used to moving around freely, so his stall was very easy to pick!
But he was always very private about his elimination. I had him for 18 years, and he hardly ever pooped under saddle or in a halter, and only once did he urinate in “public” — when I had had him out for a long time and was talking to friends while he was still tacked up. He always waited till he was back in his stall.
With my next horse I learned more about horse behavior. Tally would sniff at manure on the trail and after a couple of steps would make his own deposit. He was pretty alpha.
My present horse used to be a show horse — Maine Morgan Fine Harness Champion, circa 2007! — but he poops wherever. Seems to make a point of doing it while on the cross-ties. But when I got him he was fastidious about his person — he just didn’t get dirty. The other horses (they are out in a paddock 24/7) would be muddy and his coat would be pristine! He’s loosened up a lot and will now allow some dirt, but he is still usually the cleanest horse in the herd. He’ll do anything to avoid getting his feet wet, however. Once out on the trail he gathered himself to try to jump a 20-foot pond rather then follow the others wading in. I pulled him back and we took the long way around instead.
They are all characters, aren’t they!
Your theory is interesting. However to add to it. I had a Standardbred gelding that I adopted for a racing stable. Jimmy was a big horse in a 10×10 stall. he did all his business in one corner. It was a huge pile but it was all in one spot. When I brought him home and he was turned out he still pooped in one area of the corral. When he went in the field he wasn’t so fussy. Out of the other horses in the stable there was a mare that also did everything in a row along the back wall. Never a poop anywhere else.
Most of the others even the 2 yr olds were not particularly messy. However the stalls were cleaned every day. I can see leaving horses in dirty stabling would encourage them to be messy. Unfortunately my other horses were not so good. One of my mares would come in from the field to poop in the open barn. Go figure.