Just to add to the stats, in case it's helpful for anyone else.
Hetzer has been on chicken wings only for the last four days and his crap has become nice and firm, looks fibrous and even when squished between finger and thumb (in a bag of course...ew!) holds together. It looks like what you'd expect to find laying around in the wild. He eats the lot, there's usually one small piece of bone left. One wing in the morning lasts him until around 1pm, another at 5ish is done by midnight.
We bought a whole rabbit, skinned, gutted, de-headed & footed. He devoured the first foreleg he was given but turned his nose up at the second one next morning. That might have been because it was accompanied by some loose flesh and fat too, some of which looked to have some rabbit crap in it. Which is a shame, because I have access to some rabbit-plagued land and was thinking of buying a cheap air-rifle & scope. Maybe he would go for a whole fresh one, fur and all?
Frozen mice aren't cheap, daily cost of feeding him those looks to be over a quid.
Still not sure about all this supplement malarkey, but I'm a bit worried that as a chicken wing isn't 'The Whole Animal' he might be missing something vital. I'm going to ask the butcher if chicken heads are available, though that's going to be a bit gross on the kitchen floor, especially if my son does what he does with fish..."Can I get the eye out mum?"
Anyway, looks like we've sorted out his guts.