Aside from that, it sounds like you are doing everything right. The best way to draw realistic horses is to study real horses or pictures of horses and draw them in many different poses. Doing all of those drawings will help to train your mind to understand the shape of the horse and how horse skin and muscles and bones and joints connect and move. After many drawings you can start to create believable poses based on the knowledge that is in your mind.
You could try looking for 3D horse figurines that you can then place in the desired position. The best ones would be the collectible kind, which are usually very anatomical. I have bought one of them and they came in hand for some of my work. [link][link]