Protect his Kidneys; Try Tough Love
My mother took in a throw away dog. He will eat only table scraps and cat food. When she first got him he would get constipation. She would feed him applesauce and he would get better. Now he seems to have gotten used to the cat food. My mother had tried every dry and can dog food but the dog will not eat. I have even tried doggy treats. He seems happy and healthy otherwise.
Your mom is a decent human being; she did the right thing by adopting this homeless dog. In the process he’s learned to enjoy food that isn’t healthy for him. Cats and dogs are physiologically quite different. Cats require a higher protein diet, amounts that can lead to chronic kidney failure in dogs.
Dogs do best on a complete and balanced dry canine-specific diet. If your mom’s veterinarian pronounces her dog healthy, simply waiting for him to get hungry should convince him that high quality dog food actually tastes pretty good. Sometimes tough love is the right path to good health.