Feed them nourishing foods, I used Friskies Dry for my cat mostly but now I sometime change around as long as it is a good cat food for their age and I add tuna to dry food at times if her appetite seems to be bad. She got an allergy years ago and having sore eyes my daughter told me to use contact lens drops (ones that you can put in the eye not just for lenses) and it not only healed her eyes, it stopped her wheezing and I think it increased her appetite because she smelled food better. I chop garlic now and then real fine and mix with tuna, it is healthy for your cat as well as you. Good for heart and worms.Oh and she is now 16 years old. Her picture is in my hubs a couple times with tips.