Thanks for all your comments. Bit of a bad night as him trotting around all night was quite noisy!
I think it's definitely more terribly uncomfortable more than painful. He's been out for a walk this morning and can walk perfectly ok but sits down quite often looking uncomfortable and annoyed! Where they shaved his rear end looks a bit sore, I think they have grazed his skin in a few places so that's going to be an irritation. The wound itself looks fine, in fact I can't see anything apart from the anus being a bit redder than usual..............he doesn't have the baboon bum as being a liver roan his skin is darker, not pink!
Will see how things go today, the vet doesn't particularly want to give him tramadol if he can avoid it as apparently it can cause constipation........will update later. Thanks again.
Lianne