I guess this was probably meant for the Nightmare challenge. I shall comment as though it was, but won't leave a score.
By choosing a horse as your subject you are making a clever pun on the word nightmare. The choice of b&w (or duo-tone? - a bit hazy on the technicalities here) is good to illustrate nightmares as it somehow separates the scene out from reality (although there is a dichotomy here as this clearly IS reality..). The photo is well composed, adhering to the rule of thirds whilst maintaining a sparseness that concentrates the viewers mind on the pain and seeming never-ending discomfort that the horse is experiencing. The photo lacks 'punch', which is a problem with it as a stand-alone photograph, but actually in terms of the challenge is apt, as from my experience the visual elements of dreams and nightmares lac the clarity of reality.