Nice contrast with the green and yellows. Horse angle and black hill thing detract from it. (The "hill" is apparently an optical illusion where my eye merged the tail into the shadow to put them both behind the fence -- It could just be me :) )
Fairly well composed, good colors and detail, interesting action. It's not really grabbing me for some reason, but I can't nail down why. I'll get back to this and update if it hits me what it is.