Don't make your boar's holding pen too small. Boar will only breed when their environment is large enough to support an increase in their population. Find or push 2 boar fairly close together then throw down a sufficient stack of foodstuffs, at least one item each (food should be in small stacks, as this will make boar come close to one another to feed, close proximity to one another triggers the breeding mechanism). The only enjoin coitus after each has eaten and is happy. As long as they are not agitated, have fed and are happy they will breed, even with a diminished health pool. Often time after eating, an injured boar's health pool will restore itself completely, the odd time it will only restore a portion, rarely it will appear as if they gained little or no health. They will breed, and can produce offspring even with a less than full health pool. This applies to boar, lox & wolves.