This is a weaning ring.
It is something you will see from time to time on calves or even adult cows because they continue to nurse their dams (or other cows or themselves, actually) after a reasonable time period.
Folks do not realize that cattle will sometimes try to nurse for years. . . pulling their dams down in condition and causing issues if the cow is bred back.
Sometimes they are so persistent, even the mothers cannot be rough enough to deter them.
That is when a weaning ring can come in handy if separation isn't possible.
They are sometimes shown as torture devices by activists who do not understand or even try to find out why they are used.
They simply go in the nose and stay, for the most part, with no real pressure or discomfort in the nose. They can have spikes outside or not. The spikes deter the cows from allowing nursing to occur.
These are used in all breeds, not just in dairy. They are not used for keeping calves of the age to need to nurse from having the milk they need.
Now you know