hey man! I made a horse a while back. It's quite difficult isn't it?
Anyways, you can see my end results on my portfolio if you want.
I can tell that for your first pass you used that anatomy reference off the web from some famous artist. That's a good place to start, but like others have mentioned, it won't give you realistic end results.
It looks like you are going in the correct direction though. The key is to have lots of references from every angle imaginable, then decide which shapes and forms you are going to go with. You really have to balance the mass carefully in order to give him a real sense of weight. put a lot of mass in the torso area, and much smaller legs. The neck and butt should probably appear to be bulging out the most, then the front upper legs.
At the moment the head needs a lot of work imo, but you are probably going to get to that later.
Just keep playing around with the forms. It will take a while but you will get it.