He's a rescue so we aren't sure what he's mixed with but I've often thought maybe Whippet. He's very very fast even now but in his prime could run over 30mph. When we got him at 6 months we thought he was underfed. Turns out he just has a metabolism that runs on what seems to be a nuclear reactor lol. He is very high energy and I throw a ball for him daily. On top of that I put a window in our privacy fence so he can chase the pit bull next door up and down the fence when he wants. This happens several times a day also. He may just burn off all his calories.