This is not the same as a general category for either books or recipes, but when we index recipes that are aimed at others than humans, we generally add "[for dogs]", "[for cats]", or other descriptor to indicate who the recipe is for. This search came up with 137 individual recipes for dogs, although most of them are baked goods.
I also did a search on "dogs" in the EYB Library and see that none of the books devoted to foods for dogs have been indexed.
I hope your dogs thrive on whatever you come up with for them!