YOur understanding of the porportion of thehrose is good, in the body, but the head needs to be quite a bit larger.
IN the second drawing it's a bit confusing spatially how the horses fit together. The one on the left must be slightly in front of the other because the right hand one's leg is kind of going under the body of the left hand one. Just a bit odd there. I think it's because the left hand one's left foreleg is not going back into the page as it should . YOu have to use more foreshortening.
Do you know how to draw and use foreshortening? This is really hard to do but it makes things look like they are going straght back away from you or running straight toward you. It takes really looking at the image you are drawing from , if you are drawing from an image, and measuring mentally how long line appear,not how long they are in reality.
For example, the foreleg is actually about an inch lone perhaps when drawn from the side (in the scale you are drawing, ok?) but if you are looking at that leg from the frontish side angle, that inch becomes a half inch or less, depending on how much in front you are.
So, that front leg needs to be shortened to make it be in line with the rest of the body.
If you are doing these from your head, then I would say that you are doing a bang up job and just doing more and more will help you to slowly correct things that don't quite read right.
Horses in movement are very challenging to draw.