So back in an older world I had these two tamed hogs on herbivore island, and I kept them on wander inside a fairly large pen. I didn't really know how breeding worked at the time, but eventually when I figured it out, I went to neuter both of them, because I didn't want any more. As it turned out, my female was already pregnant at the time of being neutered. I did not know this. Fast forward a bit and there's a baby hog in my enclosure.

Basically, hog immaculate conception. I named him Butters.