I've shot a couple of feral dogs down on a big ranch in south Texas because there was no doubt they were not a pet and they were running deer. I've only shot one cat in all my 60 years in the field and it lacked a collar and was obviously hunting on our private property where we were rabbit hunting with our beagles at the time. If we're talking about dogs and cats running loose in the neighborhood we live in, then it's best to find out who their owner is, if possible, because it's their fault the animal is running at large and not the animal that should suffer.