If You Want Healthy Cows Feed Them Magnets

I saw an article on the internet claiming “If you want healthy cows feed them magnets” and I thought “oh no, not more biomagnetism nonsense.” First magnets in shoes to relieve foot pain, then magnetic bracelets for arthritis, and finally “biomagnetic therapy” for all sorts of disorders; I thought it couldn’t get worse, but feeding magnets to heifers? Really? Sounds like bull to me.

A drawing of a cow
with a magnet in its stomach.

Well, I can’t vouch for the accuracy of this story or the effectiveness of the treatment, but at least the mechanism underlying the feeding of magnets to cows is plausible. Cattle swallow a lot of junk while eating, including some that is magnetic (for example, wires and nails...yikes!). The article says

That's where magnets come in. A magnet about the size and shape of a finger is placed inside a bolus gun, essentially a long tube that ensures the magnet goes down the cow's throat. Then it settles in the reticulum, collecting any stray pieces of metal. The magnets, which cost a few bucks a pop, can also be placed preventatively. To check if a cow already has a magnet, farmers use a compass.

Apparently the “bolus gun” is inserted through the mouth; I wasn’t so sure. Wikipedia has a page about cow magnets, titled “hardware disease.” Companies make money selling cow magnets (these are big magnets, about four inches long). But even though calves eat magnets, kids should not (note the plural: the problems arise when magnets interact).

Consider a spherical cow.

The 4th edition of Intermediate Physics for Medicine and Biology has an entire chapter about biomagnetism, but no mention of magnets in bovine stomachs. What is wrong with Russ and me? The only place we mention cattle at all is in Homework Problem 30 in Chapter 4, where we analyze the temperature distribution throughout a spherical cow. A small-scale analogy of magnets in steers’ stomachs are rows of magnetosomes in magnetotactic bacteria (see Fig. 8.25 in IPMB), but I doubt the bacteria use them to collect nails before they can puncture their membrane. Yet, could we misunderstand the biological purpose of magnetosomes?

Finally, I have some good news and bad news about the 5th edition of IPMB. The good news: we submitted the page proofs and the book should be published in the next few months. The bad news: no more mention of livestock in the revised edition.

If you want healthy cows feed them magnets.