When you first decide you want a black background portrait, you need to find a photographer who can do that. There are special techniques that are used in creating that perfectly blended background. The first is the horse. They obviously need to be clean, but posed the right way. I love seeing this angled pose on horses but there are several others that work beautifully. You can decide which pose you like best and talk with the photographer about them before you start.
Turning the background black
There are several ways you can edit the background from coloring it with a pen tool to cutting out the subject and placing it into a new background. I have used three different ways before I settled on my favorite style. The main thing to consider when creating the gradient is making it look natural. You want the photo to look like you took the photograph with the horse standing in front of a black sheet. Another thing to consider when creating this look is the shadows and vibrancy on the horse. It takes more editing on the horse's body than one might imagine, and that's how you come up with a beautifully colored horse like he just stepped out of a magazine. The model horse here, Drama, looks dull in the original photo, but when you see him in a show or around the barn, he is just as flashy as he is in the finished photograph. I just played around with some colors to make it look as natural and beautiful as he really is.
The finished result
The last thing to think about is the clothes your horse is wearing. Here, Drama is wearing his jumper bridle which had some reins attached, but to clean up the image, I removed the reins. One last thing I did to make the image complete, was to brighten and shine up his eye. It's not much but it helps bring everything together. Photographing black background portraits is an art and can be really fun to do. You just need to put your creative hat on and go to work!