I buy horses and train them up, to sell them fully BLUPed for others. I particularly try to advance rare breeds in the game. I have a donkey breeding farm as well.

I also like to purchase horses that would otherwise go to the safe haven. I don't like the safe haven, as it permanently arrests a horse's game potential. 

If you are interested in any of my horses or a covering, just message me, and I'll gladly negotiate a sale with you.