Why is a calf soemtimes made to swallow a magnet right after it is born?

Answer 1

This is to prevent what is called hardware disease. Hardware disease is what happens when a cow swallows a piece of metal such as a nail or something, this can cause major problems to their digestive systems.

The magnet sits on the bottom of their throat and will catch any foreign metal objects before it causes any damage, the magnet will never have to be replace and is never taken through their digestive system.