We've had 3 'dumped' Irish dogs, A Lurcher, a Greyhound and a Whippet. One was old, one was slow, one had no prey drive. All 3 had been starved and then put on the motorway. They were too weak to run away from the traffic. Its a pikey trick is that. All 3 lived happy lives with us and we fattened them up to a proper sighthound weight.
Animal cruelty makes me sick. Dogs are generally loyal animals and being dumped by their previous owners is upsetting for them. Dogs will often stay close to where they are dumped so they are close by for when their 'owners' return for them (not that they ever do). We have found a fair few dumped dogs, over the years. Its never nice. I am not wild about taking them to the RSPCA either, not with their 7 day policy. I try and get them into independent, no kill, shelters. I've even kept a couple myself.