I have a two year old Bloodhound/Lab mix... he stands about 26 inches to shoulder. He only weighs about 70 pounds. Although the vet says this is within a normal range.. I know he is far too thin. I can see his ribs and pelvic bones. I got him from a shelter and have only had him about two months, he hasn't gained anything that noticeable. He does not have worms.. He eats just fine... more than most actually. He mostly sleeps through the day and I take him to the dog park if it is nice out-otherwise we play with him in the house. What can I do to help him gain more weight?