This is incorrect.
The only thing they are concerned with is if the food you bring has beef and beef byproducts in it, due to the whole overreaction over mad cow disease found in Alberta a few years back. After the Canadian investigators traced the sick cows back to Montana originally, the US conveniently ignored this fact. heh
Anyhow, I took my dogs across a couple times, the ONLY thing they cared about with the food was beef content, nothing else, if it had any, I would have had to ditch it. (was lamb and chicken yay)