“NITARSONE is an organoarsenic compound that is used in poultry production as a feed additive to increase weight gain, improve feed efficiency, and prevent blackhead disease. It is marketed as Histostat by Zoetis, a publicly traded subsidiary of Pfizer.” This is the remaining poultry arsenical growth promotor allowed on the US market today.
http://en.m.wikipedia.org/wiki/Nitarsone