I have seen many,many sites about horrendous pollution from animal manure getting into rivers. And many sites about unpleasant surprises from its long persistence in soil in some places. I remember reading in TIME magazine a very long time ago about a beef farm in Central Valley, CA, that had a pile of manure so high it could be seen from many miles away. Nobody wanted it. And the dopey organic enthusiasts never bother to mention that manure is seriously deficient in phosphate but too high in nitrate. Plus being full of weed seeds.