The closest that I have come to drawing in about twenty years of gun carry was due to dogs running at my daughter and her mother. About the time I had my hand on the grip their demeanor changed from pack to tongue-lolling and greeting.
I would not hesitate to kill any beast. The law might frown on discharge of a gun in your community and the owner might try action for tort loss of his beast. SCROOM It is a beast at large.
Making man and beast somehow equivalent is a much shorter road to hell than asking "what-if."