Sounds retarded on the face of it.

There no utility in fertilizing with babies or feeding them to pigs.

One, corpses don't make good fertilizer and people only ever use them (animals) because it's cheaper than paying someone to take it away. You still have to chop it up as well and it attracts scavengers to your farm.

Two, pigs eat anything, that's the point. You don't need to feed them a baby, they'll literally eat shit.

The only reason people might do this is if someone paid them to take the baby but, if there were no records, why wouldn't unwanted children just be left in the woods to be eaten by the abundant wolves of medieval France?