I really like the idea behind this. There are are a few things that, in my opinion, could be fixed.

Firstly, I can see that you needed to re-draw the hoof on the white horse in the air, however it's a bit dark and stands out. I would use a slightly lighter color. Kinda of a grayish color.

Second, (Please excuse me if this is your method fro drawing manes and tails.) the colors on the bay horses' mane and tail are white, black and grey, not shades of brown, like his actual tail would be. I use the color picker tool to get the right shades. Also, I use a much smaller brush. I'm not sure what program you use (I'm sure you've told me, but I don't remember) but most programs have an option to change the angle of the brush, and fade, which it what I do. And I also use a 1 px brush, which helps it look more natural. The same goes for the white horse as well.

Lastly, when I do wings I like to use a fuzzy eraser brush to kind of blend them with the horse, although using a hard brush works well sometimes.

Over all, good job! I love how it looks like they are dancing! <3