I'd like to add (from experience) if you have a dog (probably same with cats, but I don't know ) that has a hard time keeping on wieght I would suggest changing to somthing natural, I had Jenny on Iams and it seemed the more of it you fed her, the more wieght she lost.

*note: Do not use this method to try and loose weight, I've tried it, IAMS is horrible tasting, it's dry really crunchy and very salty. VERY bland. (yes, I taste test Jenny's food. )