Stan says, whatever he gets, depends on who's selling them. He puts them in every cow if there seems to be a lot of problems, but usually just when he suspects a case of hardware. You only have to do it once - they aren't likely to pass. The chopper has a metal alert, the feed cart has a magnet, we try to be careful.
Where do we get them? American Vet, NASCO, the vet, the local feed mill