Oh dear hope he's ok..
When I took Harry in the nurse gave me some free samples of Royal Canin that was particularly suited to a young neutered male. There were many different types for different ages and stages and she mentioned that the male post-neuter stuff was suitable for both but the female stuff didn't contain the right nutrients for the post-neuter male...
Anyway I'm not promoting the brand particularly but what it did make me think is our lil boys' nutritional needs have probably changed almost instantly with the changing hormone levels and so maybe the diet which been working fine for him before may suddenly be too much.

I wish someone else would come and post on this thread and give you some better advice than I can! We've been a bit abandoned..
xxx