By adopting them!
He's not just donating money or starting a charity, he is really actively helping horses.
Two specific horses, Whisper and Traveler, a stallion and a mare, were recently rescued from their owner for neglect.
The two horses were severely underweight and Whisper had burns on his back from where the owner tried to burn off a fungus.
The were taken in by LEARN (Livestock and Equine Awareness and Rescue Network) and have already gained a good deal of weight.
The horse's owner has been charged with:
"[…] three counts of failure to provide care or treatment for a diseased or injured animal; three counts of failure to provide humane treatment to animals; and one count of failure to provide adequate food and water."
Good thing Willie found out about the horses and is willing to take them in and treat them to the good life.
(And don't worry, the above pic is Whisper at his worst. He's gotten much better since then.)
Way to go, Willie!