Here you go: Horse slaughter conditions in Mexico explored by AAEP group - March 1, 2009
"Overall, the group's assessment of the trip concluded that both plants use captive bolt in a humane and efficient manner, and the horses were well-cared-for and properly handled
For me, the problem with the closed slaughter plants is not slaughter methods in Canada or Mexico, it is people holding onto horses they normally would have sent to slaughter for whatever reason despite their poor financial situation which results in more suffering than the actual slaughter plants...
Who is the organization? For both sides of the argument, usually there is a bias. I have never heard of and highly doubt horses are getting their heads lobbed off with a chain saw. If it happens, it is in tiny independent and un-regulated slaughter plants and is not the norm.