Also mineral deficiencies in the pigs diets have been shown in studies in the 1950's to cause digging. Good hog pastures include legumes, vegetative grass, and brassicas. Pigs cannot bloat on pasture, therefore the best pasture would be a mix of legumes. Alfalfa works well. Clovers like Red, ladino, Kura, and alsike work good.
Chicory also works well.
Rape is an excellent annual hog pasture. Grasses work best for farrowing lots because they keep down the mud. If you are planting pasture for just pigs stick with mainly legumes. They are a lot easier to manage than grass for an animal that doesn't bloat. High percentage of grass in pasture will require keeping it very short for it to be palatable to pigs.