In former times, the male luck-pig, the "Glückseber" was worshipped by some Germanic tribes. First no lucky pigs were allowed to be slaughtered, so the females were hunted until it almost happened that the lucky pigs did not get any successors. The lucky pig was left in peace from then on. Later a pig was regarded as a sign of prosperity, and on New Year's Eve they gave each other a lucky pig.
A mother sow gives birth to about 10 piglets at one birth and can piglet about 2 times a year. So there can quickly be plenty of pigs in the barn. The bristle cattle was therefore in former times a sign of wealth, success and luck. Therefore, give away the key ring piglet.
Who in the history of mankind had a pig, hardly had to suffer from hunger. As a modest Allivore, a piglet can easily be fed to a sow with plenty of bacon. This is another reason why pigs were considered lucky charms in many societies all over the world.
While in the past it was a good custom to give a live piglet on New Year's Eve, this is very rare today. In symbolic remembrance of the old custom a felt key ring is given to the pig.