Feed & breed. Simplest successful breed: place 2 portions of food near 2 adjacent boars so they come together to consume. Copulation usually takes place when boars come together after eating. I make square boar pens and throw 4-8 stax of food into the corners so that when they feed they are forced into close proximity to one another.

Feed them before nightfall as long as you are sleeping within proximity distance of your boars. Having a boar pen within alert distance of ones bed rest location is extremely advantageous, as they will breed and reproduce while sleeping. The other option is to feed them in the morning just before you engage in some activity within alert detection distance of your singular of boars, such as crop planting. I place small plots of garden within my boar pens, then will turn off auto pickup when harvesting my crops. I have a small breeding area right next to my bed rest location, separate but attached to my larger boar pen. The more space boar have the more likely they are to reproduce. When boar are cramped and tightly packed together they are less likely to reproduce.