The thing to do is, when the piglets are a few weeks old, Birth Notify the BPA, this just means that you tell them there was a litter of, say 11, six females and 5 males.
You will not be issued with any pedigree papers, but the birth will be assigned to the sow, and you will be entitled to the eleven pedigrees, should you, or the people you sell the piglets to, want to buy them.
Then, when it comes to selling them, if customers only want them for meat (say the five males) then you do not need to pay for the pedigrees, but they still count towards the litters that your sow had delivered and reared.
If you wish to breed from the girls, then send off for the pedigrees for the ones you are keeping, or selling as pedigrees.
Hope this helps
Julie