What is the habitat of horse?
The habitat of a wild horse or pony is across open land like fields , woods , mountains ,forests and even desserts! tamed horses , however, lived as wild horses but now live in closed fields or stables. I hope this comes to use of you!
"feral thoroughbred horse" is very nearly an oxymoron. A thoroughbred must, by definition, be bred in captivity. Asking where the habitat of something that cannot exist is is rather pointless. It's possible that a thoroughbred horse could escape, but its habitat would then be "somewhere around where it used to live, probably" which is not really very informative.