The death and destruction of the innocent lives of horses is laid out in grisly detail by Animal Angels in this report on their investigation of Natural Valley Farms in Saskatchewan, Canada.
It is in pdf format, and can be accessed at this link:
Please be warned there are numerous graphic images contained therein.
The atrocities related to horse slaughter seem to have no end. How anyone can defend it seems beyond the scope of any reasoning, and one has to closely question the motives of those who do.