I read "Animals in Translation" by Dr.Temple Grandin last year. A very interesting read. She is autistic and says she thinks in visual images. In the chapter "Her Story" she writes "During my thinking process I have no words in my head at all, just pictures."
For someone who is the expert in her field on humane handling (slaughtering) systems (she's been designing these systems in the meat packing industry for thirty years and over half the processing plants in North America use them) when she says "My worst nightmare has happened", you have to appreciate where this statement is coming from.
On one hand I am glad that horses will no longer be slaughtered in the US.. on the other hand we simply have shifted the slaughtering to Canada and to Mexico. And lengthened the time in transit these doomed animals will now spend, a slow ride to slaughter.
Eliminating or reducing horse breeding will take time. We have the same problem with unwanted cats and dogs here in Canada. At least we don't have to ship them hundreds to thousands of miles away to meet their fate in another country. Irresponsible owners won't care regardless. Be it horse, dog or cat, rabbit or reptile.
http://www.grandin.com/references/handle.stress.html Assessment of Stress During Handling and Transport
http://www.grandin.com/references/horse.transport.html Study in 1998.
"Welfare problems in slaughter horses are listed in order of priority: It is the authors' opinion that the top ranked problem causes the most suffering.
1) Conditions caused by owner abuse or neglect.
2) Injuries due to fighting when strange horses are mixed in the marketing and transport channels.
3) Injuries directly attributed to the design of the trailer."