Somebody 说:
You've never been on a beach with your horse and Old Spice then. It shouldn't be happening, unless it's the horses that you started out with, then it can get random modifiers (along with all other items in the starting kit). You should be able to talk to the relevant merchant for any item and get a bad modifier removed, but good modifiers will never come back. Is it only happening for the horse you're riding, all horses of that type, or a horse in a specific slot in your inventory?
I recently bought a spirited hunter on day 25 or so (not starting gear) and after a while it turns "smelly." When this happens, I reload my last save and it goes away for a little while, only to turn "smelly" again. Also, I gave Klethi a steppe horse that I bought (she's in my party) and it randomly turned "Champion"

The difference is her horse changed and stayed that way, mine keeps becoming smelly.
Also, this happened earlier in the same game with another horse of mine, but I figured it was related to some kind of injury associated with a random event (though maybe I'm thinking of Brytenwalda, a different mod, when I say "random event") so I sold it.
Also Also, horses in my inventory seem to become smelly randomly.
Maybe it's that rotten cheese I'm carrying?