I recently came across a study on choke chains done in 1992. The findings concluded that choke collars can damage the cervical sympathetic nerve, the neck and back vertebrae, and cause foreleg paralysis among other things.
I personally believe collars should only be used as a place to hang a dog's tags. And with all the accessories available today that work on principles other than brute force, there's really no valid reason to use a choke collar.
I am a strong advocate of head collars and harnesses (perhaps that's another blog) although you should talk with a certified trainer before attempting to train with either.
For more information on the study, search for 1992, Sweden, and Hallgreen.
