I have a senior that is pretty picky about stuff added to his feed, also. So, since his senior feed is pelleted, I try to find pelleted supplements to mix in (so far, he just gets a basic joint supplement and that seems to be working just fine for him), they are harder for him to sort out and he'll usually eat them. Powders, granulars and liquids he is not fond of and will sort them from his senior feed. He also isn't fond of wet feed, so that makes it harder to mix in supplements and another reason I go with the pelleted products.
