For a historical perspective on raising pigs, "Harris on the Pig" is the best. Harris's first edition appeared in 1870. He was an incredible biologist. One of my favorite parts read:
Of the desirable qualities in a pig, therefore, a vigorous appetite is of the first importance. A hog that will not eat, is of no more use than a mill that will not grind. And it is undoubtedly true that the more a pig will eat in proportion to its size, provided he can digest and assimilate it, the more profitable he will prove.