For a senior dog that needs weight loss and has arthritis, the Hills metabolic and mobility diet is a great option. It is a prescription diet and comes in dry and canned food. They also make treats or the pet parent can opt for veggies or lean chicken in small bites. Ask your veterinarian about a good glucosamine chondroitin supplement for arthritis. It is worth looking into adding essential fatty acids as well to your dog’s diet. Again, consult your veterinarian for recommendations. Keep in mind that these can add calories to your dog’s diet so you need to be mindful when adding new supplements or treats to your dog’s diet and adjust feeding accordingly. Your vet is your best resource for more information.