How do you turn a girl horse into a boy horse on My Horse app

I have played this app on my ipod toutch for about a year... I have all the horses unlocked and all the tack and food etc... I dont think that you can turn a mare into a stallion... From what I know of you can buy another horse that looks exactly like your horse in the different gender... But I really dont think that you can change the gender... Hope this helps

-Love Okapi