Zombie horse, from Con's Recount of the Apocalypse

(taken from the sketchbook of Con Robert Olmstead, a survivor whose whereabouts are unknown, presumed dead. He documented a lot of the apocalypse with pencil including writing and many drawings. His description of the work was found on the preceding page, and is as follows:)
Of the many animals the strain of the disease has mutated to infect, the horse is probably one of the most terrifying. My sketch shows one of the 'cleaner' infected horses, as in most of the skin is falling off but does not look as infected, rotting or grotesque as some of the human zombies. My guess is that the virus strain for horses causes much of the body to deteriorate, starting with the skin, which weakens and tears easily when brushed against trees. The hole in the skin then continues to open naturally, exposing muscle to flies and to the environment which also starts to deteriorate. Judging by the entrails which have started to fall free from the body, I assume the tissues holding them in place are deteriorating as well. His belly was most likely sliced open when he attempted to jump over something. The creature appeared to be in a lot of pain, or possible there was a problem with its lungs, it was constantly wheezing and grunting and whinnying(loudly, I could hear it all from a distance) but still moved normally, if not stumbling ever so slightly. I witnessed this horse from my binoculars. I had been near this pasture in the past and there had been no such livestock, but this horse continuously returned for some reason. I wonder if part of it's memory is still intact and it just instinctively returns to where it was most familiar when it was not infected.