I already know nobody is going to click on OP’s link, so the short version is the magnet is permanently placed down in the cow’s second stomach and it stays there for life, and if the cow eats and nails or pieces of barbed wire, it sticks to the magnet instead of shredding up their intestines.

Thats actually fascinating.

Wait until you learn about portholes to their stomachs and methane vents people install on cows.