Law vs Breed: why didn't Law use room to remove collars? Law's room ability is a very strong technique, and he can use it to slice whatever he wants.  Why doesn't he use it when fighting against Breed to remove collars from other animal and chopper?

I don't know the chapter but it's on episode 626.

Here is a YouTube link.
It was a filler episode which is not taken from source material (i.e. manga). The fillers are just to extend time for the anime so that it does not catch up to the manga.

This happens in Naruto quite a lot and One Piece has only three filler arcs, so don't think too much about that episode, as it is there only to extend time