Adding gilts to the drift:
Neither the United States Department of Agriculture nor the National Pork Producers Council has data on the number of pastured pigs, though in 2006, research done at Iowa State University estimated that the drift, as a group of pigs is known, numbered from 500,000 to 750,000.
Several factors are driving the appetite for pasture-raised pork, grocers and chefs say. Consumers are increasingly aware of and concerned about the conditions under which livestock is raised, and somewhat more willing to pay higher prices for meat certified to have come from animals that were humanely raised.
The rest of the article has lots of stuff on the market for pigs, hogs and parts (e.g., a half-head salad) and some great jargon (adding gilts to the drift).