The happiest pigs I ever saw lived in the Bolivian Chaco, that semi-arid, lowland region in the southeast of the country. Every day, the villagers would let their pigs loose, to roam. The pigs, a tough little local breed, would wander off in troops, eating refuse on paths, scavenging in harvested maize fields or in forest remnants. At the end of the day they eagerly trotted home in anticipation of getting a trough of lawa, a thin maize soup that their owners cooked for them. Then the pigs were safely shut up in their pens for the night. It was a low-input system, and not very productive. Sometimes the pigs could get run over by a truck, or get killed by dogs. But they also put on weight slowly, as all that outdoor exercise kept them skinny.