OK.. here is how he is bow legged behind. Not cow hocked. His hind feet point straight forward forcing his hocks OUT. See the red lines. The blue lines show approximately how the feet should point. The hind leg is a spiral construction (like a spring). So the hind feet need to point out to accommodate that physics.
I LOVE this horse's expression and head.. circled his head in green for that reason.
The shoulder is lovely because it lays back and has a nice open angle at the point of shoulder from scapula to humerus. A lot of quarterhorses have a closed angle at the point of shoulder. He is tied at the knee and light boned.. arrows to show this. And the marks on his back to show the long coupling. I wish the peak of croup were further forward between the two lines on his back.