Name: Duncan M.
Why are cow magnets used? What happens once the cow has swallowed the magnet?
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
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 magnet.
Laura Hungerford, DVM, MPH, PhD
Department of Epidemiology and Preventive Medicine
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Update: June 2012