Beekissed
Mountain Sage
That toxin is produced by the actual tree roots, with only minimal amounts to be found in leaves and hut hulls, and won't be a problem after processed through a pig's gut.
Its roots, which may extend 50 feet or more from the trunk, exude a natural herbicide known as juglone that prevents many plants from growing within their reach. Tomatoes, potatoes, apples, pears, berries, and some landscape plants such as rhododendrons, azaleas, and lilacs may be killed or stunted if grown in close proximity to black walnut roots.
Minor amounts of juglone are supposedly generated in several other ways: by leaf decay on the soil surface, from nut husks, and even from rain water dripping through the leaf canopy. The quantity generated by these other means, however, is small. In addition, juglone is not very water soluble, so it will not move far in the soil.