Here is my try on a full horse skeleton as I wasn't pleased with the non accurate models I could find.
I created this model based on a lot of veterinary anatomy books and a lot of bones pictures and under the supervision of equine veterinaries for the model to be the most accurate possible.
I'm not specalised in rigging, however you should be able to get some nice results with the blender file as seen on the screenshots.
You can use it to teach about equine anatomy or for animation.
You can use this model to get some nice closeups of the joints and some complex parts of the bones, even from the inside bones of the skull.
Please note that as it is a custom rig, the .fbx couldn't get everything right so the best for animation is to open the blender file directly, or you can simplify it or modify the rig depending on wich software you want to open it.