Purina foods is doing the testing...as my supplier is owned by them. I agree with you when they told me what is was I asked the same question. That is why the Food and Drug Admin is involved...I am still piecing this together. But if I had to guess the grain used was from one of those batches of bad grain from last year. I received the batch in Dec...which means it was pry made in Oct/Nov....so it is very possible the grain came in earlier.
The world may never know...or at least I may never know.