A cow magnet is a preventive veterinary medical device for cattle

Cattle

Cattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...

. Traditionally, cow magnets were strong alnico

Alnico

Alnico is an acronym referring to iron alloys which in addition to iron are composed primarily of aluminium , nickel and cobalt , hence al-ni-co, with the addition of copper, and sometimes titanium. Alnico alloys are ferromagnetic, with a high coercivity and are used to make permanent magnets...

 magnet

Magnet

A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets.A permanent magnet is an object...

s about 1cm by 8cm (0.4 by 3.1 inches) in the shape of a smoothed rod, but today they are more commonly several ring-shaped ferrite

Ferrite (magnet)

Ferrites are chemical compounds consisting of ceramic materials with iron oxide as their principal component. Many of them are magnetic materials and they are used to make permanent magnets, ferrite cores for transformers, and in various other applications.Many ferrites are spinels with the...

 magnets attached to a stainless-steel or plastic core, in the same shape as the single-piece original.

A rancher or dairy farmer feeds a magnet to each calf at branding time; the magnet settles in the rumen

Rumen

The rumen, also known as a paunch, forms the larger part of the reticulorumen, which is the first chamber in the alimentary canal of ruminant animals. It serves as the primary site for microbial fermentation of ingested feed...

 or reticulum

Reticulum (anatomy)

The reticulum is the second chamber in the alimentary canal of a ruminant animal. Anatomically it is considered the smaller half of the reticulorumen along with the rumen. Together these two compartments make up 84% of the volume of the total stomach. The reticulum is located between the rumen and...

 and remains there for the life of the animal.

When the cow grazes, it often consumes and swallows what is called tramp iron: baling

Baling wire

Baling wire, otherwise known as "farm wire" or "soft wire," is used in an agricultural setting and industrial setting for everything from mending fences to manually binding square bales of hay, straw, or cut grass...

 and barbed wire

Barbed wire

Barbed wire, also known as barb wire , is a type of fencing wire constructed with sharp edges or points arranged at intervals along the strand. It is used to construct inexpensive fences and is used atop walls surrounding secured property...

, staple

Staple (fastener)

A staple is a type of two-pronged fastener, usually metal, used for joining or binding materials together. Large staples might be used with a hammer or staple gun for masonry, roofing, corrugated boxes and other heavy-duty uses...

s, nails, and other metallic objects. These objects are indigestible and would lodge in the reticulum and cause inflammation

Inflammation

Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...

 resulting in lower milk production (for dairy cattle

Dairy cattle

Dairy cattle are cattle cows bred for the ability to produce large quantities of milk, from which dairy products are made. Dairy cows generally are of the species Bos taurus....

) or lower weight gain (for feeder stock

Livestock

Livestock refers to one or more domesticated animals raised in an agricultural setting to produce commodities such as food, fiber and labor. The term "livestock" as used in this article does not include poultry or farmed fish; however the inclusion of these, especially poultry, within the meaning...

). This condition is called hardware disease

Hardware disease

Hardware disease is a common term for bovine traumatic reticuloperitonitis. It is usually caused by the ingestion of a sharp, metallic object. These pieces of metal settle in the reticulum, and can irritate or penetrate the lining. It is most common in dairy cattle, but is occasionally seen in...

.

The cow magnet attracts such objects and prevents them from becoming lodged in the animal's tissue. While the resultant mass of iron remains in the cow's rumen as a pseudobezoar (an intentionally introduced bezoar

Bezoar

A bezoar is a mass found trapped in the gastrointestinal system , though it can occur in other locations. A pseudobezoar is an indigestible object introduced intentionally into the digestive system....

), it does not cause the severe problems of hardware disease. Cow magnets cannot be passed through a cow's 4th bonivial meta-colon.

Cow magnets are widely available from veterinary, feed supply, and scientific supply sources.