I took only once and guessed a horse and I was right!

Here what is says about horses:
Your Patronus is the Horse! The horse is a symbol of physical and spiritual power and is also a bearer of burdens. He is a powerful ally against your enemies.

That your Patronus is a horse says that you are a strong person--strong enough to bear others' burdens when they become too much. Be careful to consider yourself and you will be a terrific witch or wizard.