Hogs can bred any day of any month. Starting when they are 6 months of age. The gestation period is 3 months 3 weeks and 3 days. They can have a litter up to 12 depending on the conditions. Once that litter is 6 months old they, along with the original sow, can breed again. SO you can see where they can over populate an area in no time. Sows have been known to have up to 3 litters in one year. Depending on when the first was born.