Is anyone else experiencing derpy horses? I have found two horses on a map I have been playing that don't move fast at all. One of them literally walks slower than you would yourself walk in game. If need be, later I will try to get a video of what I'm talking about.
Horse speed varies, but I think what you found is weirder than that. I mounted a slow horse once too. Even his gallop was slow. I just killed him & took the leather. I guess mutation happens in mc as well as nature.