First of all, welcome to Pet Talk, and good for you for feeding a high quality food!

It is absolutely possible for a dog to develop an allergy, even to something he's been eating his entire life. There are digestive enzymes you can buy specifically for dogs that should help with the gas, and you can also go to your natural food store and pick up some natural sugar-free yogurt. My friend's dog was very gassy and they refused to switch her food --- as soon as they started giving her yogurt, the gas stopped.

Good luck! Hope you stick around and show us pictures of your dogs!