Mine was a different situation, Cody was nearly 12, it was a very confusing time. They thought he had colitis, so really wanted no diet change. He had bone cancer in one of his back legs as it turned out. Prednisone did increase his food intake for few days then went back to not eating. Looking back, I wish I would have just feed any high value food. Chicken, hamburgers whatever. I'm sure others will have better suggestions, or check with you vet. Like said, different situation. I wish the best for you and your gsd.