
If more food is coming out the other end as teh squits, if he isnt interested in eating more food, then simply, dont feed him more food.
Unless there is something physically wrong with him, he will eat what he needs (if you are feeding two/three times a day and taking it away after 10 minutes that is -- if you are free feeding you are setting yourself up for problems).
An 8 month old puppy of ANY breed should look a bit lean and gangly, less so in smaller quicker maturing breeds though, and probably more so in bigger slower maturing breeds.
Im sure some people think he should be heavier, more musculed, fatter, whatever but he IS a puppy, and as such needs to grow strong bones BEFORE putting heavy muscles on top of them.
Knock him back down to what he was on before, and gradually increase it, when he starts leaving some, thats too much. I always reckon on feeding at each meal time, about 3/4 of what he would eat if left to eat as much as he wanted.
And my 6 month old x breed is VERY gangly, all angles and ribs and huge paws, tail to teh floor etc -- let them grow the way they want to, forcing it only causes problems!
Em