If you have already discussed this with the vet at the clinic as well as the heavy handed person themself (maybe they don't realize what they are doing), and nothing is changing, unfortunately, there's not a lot you can do. IMO-find another position with another vet and be very upfront with the vet you work for now, as to exactly WHY you are leaving. I think it is admirable that you are so concerned for these animals, but if the vet isn't worried about the way they are being treated either, then it's time to move on to a clinic where things are done differently and more in line with your own moral and work ethic. Unfortunately, it's impossible to change people who don't want to change or make people see what they refuse to look at.

Bless you for being so caring! You should have no problem finding someone to appreciate the excellent qualities you obviously have!