I have had great success breeding boars. The best trick is to throw down a stack of 2 food items between 2 boar that are close enough together to detect the food. When they meet to eat they breed 90% of the time. If I see a group fairly close together, I will throw down a stack of food to equal their numbers. If there is some distance between them, push them together then feed them. I will fill my inventory slots with stacks of 2, push one boar close to another, then throw down the stack of 2 and watch the hearts throb, works like a charm.

There is an added bonus in feeding & breeding boar (lox or wolves) using this method, in that I do not have to hang around the area for long. Once the lovemaking occurs I can leave, because when heart throb occurs breeding is completed and the boar will produce offspring whether one is in the vicinity or not.