Hey Donna! My Apollo and your Duke look alike(except Apollo is fawn). They even sit the exact same way. Apollo is 2(July b-day) and he only weighs 52#. He, like Duke, is a tall skinny dog. I personally think that Apollo should put on weight, but he is not a big eater, plus he LOVES to run. I think that he could go up 10 pounds and not look so skinny, but he doesn't scarf food, so I assume he's not starving. He is a piecer. He eats a little here, a little there, plus, he has a healthy coat, he is soft, he has clear eyes, and so on and so forth. Since Duke is only 7mos., I don't know that he is underweight. Seems to me Bub(Apollo) weighed about the same at his neutering, within 5 pounds anyhow. I am curious as to the responses you get, but if he is eating and seems healthy(and vet says he's healthy), then I wouldn't worry too much. 'Course, it sounds like you and I feel the same, they could weigh more and it wouldn't hurt them, but being Duke's a puppy I would see how he develops. Good luck and happy feeding!
Erin
Apollo & Rocky's mom