Do not free feed give it small amounts of food often. if it eats too much too fast it can hurt his system. Go to your shelter bring the dog, ask if they can do anything for it at low cost and you are willing to foster or keep the dog but need help. They may at least give you food, meds if it has any infection, flea treatment, wormer. if they don't try another shelter. People working at the shelter really do want to help animals.