Hi all.

We had our cat Marley neutered on Wednesday morning. He was all right on that day. The vet prescribed Hills diet for a day or two while he'd be recovering, and then switching him to his usual food again. I didn't get the idea of this but we followed the vet's advice. Marley is usually on a grain free diet as he has a sensitive tummy.

Yesterday he ate 3 meals of Hills. In the evening he became very passive and at about 7am this morning I found him vomiting. The vomit looked like it was not digested, with a sick sweet smell. At 9am he pooped but it was gray color, stinky and soft. He didn't wish to eat this morning although he was quite lively.

I want to give him his usual grain free food today and see how he goes. If he vomits again I'll take him to a vet. Do you think it's just a feeding issue or he may have caught some virus at the vet?
I don't know why he had to be switched at all just because he was neutered, I've never heard of that. Go back to his usual grain free food immediately, I think anyway. Hill's is SO full of garbage his poor tummy probably can't take it. If his issues don't resolve within 2 to 3 days after that, then I'd say call the vet. He also could have had a bad reaction to the anesthesia so you may want to mention it to the vet anyways in order to have it on his records. But switch his food back.
I'd call the vet and tell him all that has happened and ask why he wanted to switch the food and if it's okay to give him his grain free food again. I'd also try to find another vet and consult with him. It sounds strange to me that your vet decided to change the food knowing your cat has a sensitive stomach. Neutering is a stress and food change could have made it more stressful. My cat has a sensitive stomach too and I know how frustrating it can be.
Thanks for your prompt replies. I knew I shouldn't have switched the food and I wouldn't have done it if it wasn't a vet suggesting that! I was going to give him a call but wanted to have more opinions too. Thanks again.