Alfalfa is not needed to be given to piggies at all in any form or at any age. It’s not a grass hay and is too high in calcium which can lead to bladder stones if given for too long.
Pregnant sows can have a small amount of alfalfa to boost their reserves, and newborn babies can have a very small amount of additional alfalfa but only until the babies are three weeks of age. They do not need any alfalfa after three weeks of age.
For anybody who does choose to feed the alfalfa containing young piggy pellets, then they should be stopped by the time they piggies are 4 months of age due to the higher calcium content.
Adult pellets (grass hay based) can be fed from birth and the young piggy pellets are a bit of a gimmick and never actually need to be given even to young piggies at all.
Whatever pellet brand you choose, ensure you feed only one tablespoon per pig per day.
I believe Oxbow essential are a brand which are a common brand to feed in the US. They do not contain alfalfa.