Cow magnet is 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 stray metal from the folds and crevices of the rumen and reticulum. One magnet works for the life of the cow!

Everyone thinks of the great scene of cows out grazing in a beautiful pasture.  Cows eat grass and have a really amazing multicompartmental stomach that allows them to be productive on this food source.  The bottom front part of this stomach lies against the diaphragm and the heart.
 Unfortunately, sometimes these beautiful pastures, or the barns where cows also live, can have old pieces of wire fences, nails, bits of discarded cans, etc.
 In her grazing, a cow might accidently ingest a piece of metal.  This drops to the bottom front of her stomach.  Through all the powerful churning of her digestive system as the grass is digested, these pieces of metal can work themselves through the wall of the stomach and into her lungs or heart.  Leaking digestive juices can cause infections that can be fatal to the cow.
 But for scores of years, veterinarians and farmers have known that if you have a cow swallow a large smooth magnet, the magnet will also fall to the bottom front of her stomach. It will remain here, often for years, and attract the pieces of metal so that they do not
penetrate the stomach wall.  It is not foolproof, so it is also important to make sure that there is not a lot of metal lying around.  But having seen old magnets taken from cows that died of other things, there is sometimes an amazing number of dangerous looking metal objects trapped on the magnets.
Currently, we have four types cow magnet, they are stainless steel cow magnet, block ferrite cow magnet, ring ferrite cow magnet and AlNiCo cow magnet.