Information sourced from UK Government.
All cows reared for beef receive two ear mutilations. There is no requirement for anesthesia to be used and cows are often restrained for this painful procedure.
As a form of identification cows reared for beef have tags pierced into both of their ears. This is first done before before the age of 20 days and occasionally repeated if replacement tags are needed.
A farmer performing an ear mutilation on a cow
Because of the nature of the procedure cows are usually restrained in a device known as a cattle crush.
A cows ear may also be notched. This procedure is legal, but less common. Like ear tagging it does not require anesthesia.
A cow with an ear notch