Not really having raised horses (just had Misty for a year and she was already a mature mare), I don't know a whole lot about their medical calumities, though I do know some stuff and continue to at least read about them.
One thing I noticed...the gal mentioned something about getting a mule to ride. This was not long after she said she had turned her horse out so he could urinate (my word--she was rather crude, if you know what I mean). I found that tidbit interesting but didn't bother to question further, though its my understanding that horses will urinate/defecate just about anywhere, like cattle and sheep....isn't that where 'mucking' out stalls came about?
My Dad has told me that their mules in Oklahoma always defecated in a single area in the corral.