For the most favourable boar breeding conditions, set up the boar pen in reasonably close proximity to a common bed/rest. Feed your boars an hour or two before retiring before evening descends. The sounds of piggies being born should invade the audio feed while sleeping, and the piggies will be visible when checking on your boar pen in the morning.

My boar/wolf pen is quite large, so I have created a smaller fenced in area leading up to the entrance to my building. I push 6-10 boar into the smaller pen which is about 20 metres from my Dragon Bed. Every 4 or 5 days I have to open the gate to this smaller breeding pen to release the boars beginning to overpopulate this smaller enclosure.