For a good 15+ years I have fed Hills prescription c/d to ALL my cats. I have never run across allergies or adverse effects of any kind. The only difference was that prior to c/d I had 4 cases of crystals/blockages (in 5 years), and since c/d I have only had 1 (Rutherford ended up making the calcium oxylate crystals, that blocked him. The crystals at the opposite end of the ph spectrum)

But, having said that, I have been looking into finding a food with better ingredients. Innova looks good. I am also trying Fromm. VERY good ingredients, low ash and magnesium (important for urinary tract health). Even nutro and royal canin can't compare with their ingredients.

And even after saying THAT, I am not ceertain that I will change their food. Why fix it if it ain't broke?? c/d from Hill's has been very good to my cats.