ABSTRACT
Agricultural producers worldwide are becoming increasingly concerned about the effects their practices may have on the maintenance of environmental quality; in fact, the impact of animal and crop production technologies on soil and groundwater is a primary concern of modern-day agriculture (Zebarth, 1996). Attention has focused first on nitrogen and phosphorus, which are major elements in animal wastes, and concerns have been sufficiently strong that in some areas, such as the Netherlands, nationwide reductions in animal numbers have been mandated (Cheeke, 1995). From these problem areas there has been a natural extension of interest to various other substances that are added to livestock diets, and particularly to those, such as selenium, that may contribute to a toxicity burden.
