What is the best dog food i can buy for a large dog?

Ah bless you man, I'm surprised your vet hasn't been more help on the matter. Iams is a really excellent dog food, and they even have a contact us page so you can ask about your dog's specific disease. It truly is an awful disease. I would give that a go. Good luck, let's hope you can get some good answers to help you and your furry friend.