Your pigs would have needed your own (metal) tags - or slap mark - bearing your own herd number in any case.
Some breeders attach plastic management tags for their own information, but you always need to tag with your own herd number for any additional move. Most abattoirs will insist on a metal tag or a slap mark. Some manufacturers of plastic tags say their tags will withstand the abattoir process, but you risk getting turned away at some if your tags are not metal/if you don't have a slap mark.