I absolutely adore what you've done here. This is an amazing, powerful, well composed photo.
So let's start with the technical stuff.
Great use of limited depth of field to focus on the horse and little girl. Had you used an extended depth of field the background would have been too detailed and distracting from the subjects. Having the background and foreground slightly out of focus is a great way to create a focal point in a highly textured photo that is in black and white.
The exposure is just perfect to capture the details of the texture and create depth and contrast with the shadows. The ranges of texture and variety are so interesting and beautifully captured.
Composition is extremely interesting. You fully understand the rule of thirds and the idea of supporting elements (such as the gate in the background, nice contrast to all the natural forms having some straight lines in perspective towards the subject). You've framed this picture so that both subjects are clearly the focus but have enough breathing room to be comfortable in their surroundings.
The mood is so powerful, the girl has such confidence and strength in her expression which adds a really interesting contrast to the relaxed, grazing horse. It's not awkward or weird to have her in the picture at all and I feel she adds a great layer of complexity to the picture.
I can't get over how much I love this picture, the feeling of confidence from the girl, the isolation of their environment, the relaxed posture of the horse, it all feels meaningful in how it compliments each other through contrast. The only things I can think that might be working against you is the tension between the horse's head and the lower right corner of the photo, it's slightly claustophobic but not majorly; the tilt of the camera is slightly distracting. But overall a great photo all around.