Well, we're recently back from the vet, and the doc suspects that Kuffer may have an over active thyroid. The gland in enlarged, and his general symptoms are consistent with that problem. He's had a blood test, and we'll have results in the next couple of days, and we'll take it from there. It could be an operation, or medical intervention.
This is a relief, actually, as I was fearing that Kuffer might have the same condition as Boy, who died last September. But it seems not.
Will keep you all posted on Kuffer's condition... but you'll be pleased to know he's cheery in himself and has been eating.