[kokanator]

My father worked in a slaughterhouse. The magnets were often recovered in the gut room ( the place where they process guts and hides for the rendering house ). As a result I had/have a pile of these magnets. They actually come in several different forms. I had a few that were covered with some type of plastic and a few others that simply looked like the rough magnets you might find on the back of a fridge magnet just larger. My guess is the farmer would use whatever was actually cheap and available regardless of whether they were "cow magnets".