Great job! Proportions are lovely and you have definate talent. It looks like you just have to work on the fluidity of the drawing. In the first one your shading is very fluid and believable while in the other two its more clumpy and illustrative.
Aside from that I'd prbably just say push a couple value on the first one but otherwise you did a very nice job.
Those pictures are lovely! I always found horses hard to draw for some reason...
They say horses are one of the hardest things to draw, sculpt... for an artist because of all the different sized shapes.
When I started it was really hard to get the proportions right. A persons eyes will see funny things when they do not fully understand what they are looking at. I found one of the best ways to help that was taking a number of anatomy and equine conformation classes. An artist can never know the structure of their subject too well...!!