From Habitat for Horses:
This article has been a major collaborative effort. Within these pages you will find absolute, scientific proof that horse meat from the US is deadly. To dispute these facts is to deny any role that science plays in research of the effects of chemicals on the human body. For those in the US, this tells of why a Federal system once concerned about food safety decided to bend the rules to benefit a few foreign companies.
For those in the horse meat eating countries, read closely, for this will tell you why you are not feeling well at all. While long and detailed, this knowledge is vital to those wanting to know the truth about horsemeat and drugs.