Most hog feeds I looked at have extreme overdoses of copper in them--hogs are highly resistant to copper, so it's added to their feed to improve their growth rates. The amount of copper in hog feed is high enough to just kill off sheep that get into it and eat it, for example.

While the rodents may be able to withstand these high copper levels, I am concerned for the health of any carnivore that eats those rodents. Were you able to find hog feeds that did not contain excessive copper supplements?