We have two neutered male indoor rescue cats, both 2 years old. They have been living on a dry diet, as wet food gave both of them diarrhoea as kittens. Both have regular check ups, the last one was about 2 months ago, and the vet says they're both very healthy. We wanted them to drink more water, so we got them one of those drinking fountain things, that keeps the water moving, and they drink a lot more from that than they did when they just had a bowl.
However, I read recently that dry diets can cause kidney and bladder problems, especially in male cats, so I bought some grain-free tinned cat food (they have James Wellbeloved cat biscuits). I gave them one small spoonful each, as I didn't want to upset their stomachs by giving them a bowl immediately. Cat A has eaten it, and loved it, but he will eat anything and is never sick. Cat P has thrown up six times since yesterday morning. He's sick on a fairly regular basis anyway, but this is extreme even for him. The James Wellbeloved biscuits were the least sick-inducing food we could find for him, and we've tried all sorts of brands and flavours and types, including food labelled for sensitive stomachs. The vet couldn't find anything wrong with him and said he's probably just gorging himself. I've tried putting food in two different rooms so they can eat separately, in case he's competing with Cat A to get the food down, but that's no good. They eat at the same bowl, together, or they stand at the door separating them and cry.
So what should we do? How do we balance the risk of future kidney and bladder damage with the sick, which can't be doing him any good?