From what I've been told by our American friends, indeed, melamine was the product that had contaminated the gluten used in pork feed, and recently in poultry feed in the U.S. Therefore, the ingredient was either used alone or in domestic animal feed and introduced into the cattle feed chain. This practice is illegal in Canada. In Canada, we cannot feed pork with the same feed used for cats and dogs.
On May 3rd, 2007. See this statement in context.