I have always wondered what breeds of pig are used in the preparation of bacon (esp in USA).
There is no hog that is a required breed for bacon, and you can make bacon out of just about any hog. Bacon is just a cured, smoked pork belly. They used to use Heritage breed hogs, like the Tamworth hog, to make bacon, but today they use a mixed breed hog to cover a more broad demand of different pig products. It's likely that you'll still find bacon made out of this breed of hog, but a larger brand is likely to use mixed breed which create a good balance of meat qualities in the loin, belly, ribs, and hind quarter.
Many claim that Tamworth and similar breeds produce better bacon, but I personally cannot vouch. I have never compared the 2, and I'm generally uncertain what breed of hog I'm eating most of the time.
For more reading you can see here.