Make sure the breeding area is protected by blanketing it with anti-spawn items like workbenches, wards & campfires (both can be buried. fire sources do not have to be lit) or torches. I found additionally placing workbenches up high in the trees outside of my boar/wolf pens helped a lot. Although fire no longer agitates tamed animals, it is not a good idea to have lit unprotected fires around that they might run through if they do get agitated. When there is an invasion event, make sure to run outside of any defenced areas and engage the invaders quickly. This will save damage to buildings and animals.