What are Cow Magnets? Cow magnets are popular with dairy farmers and veterinarians to help prevent Hardware Disease in cattle. While grazing cows eat everything from grass and dirt to nails staples and bits of bailing wire (referred to as tramp iron). Tramp iron tends to lodge in the honeycombed walls of the reticulum threatening the surrounding vital organs and causing irritation and inflammation known as Hardware Disease. The cow loses her appetite and decreases milk output (dairy cows) or her ability to gain weight (feeder stock). Cow magnets help prevent this disease by attracting and holding stray metal from the folds and crevices of the rumen and reticulum. One magnet works for the life of the cow!