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The beef cattle industry in the United States has been using a variety of growth-promoting steroids and steroidlike compounds (GPSCs) to improve cattle growth rates, feed efficiency, and lean muscle mass since 1954 (Raun and Preston 1997). Almost 96% of cattle placed in feedlots receive one or more GPSC treatments (USDA 2000). Although there are a number of natural steroids used as GPSCs, synthetic steroids are often more potent and biologically active than their natural analogs (Preston 1999). After administration, a portion of these natural or synthetic steroids and their metabolites are excreted into the environment either in animal feces or urine. Irrespective of GPSC treatment, animals also excrete natural endogenous steroids that also occur in feces and urine. In the United States, for example, an estimated 49, 279, and 4.9 Mg (54, 307, and 5.4 tn) of natural estrogens, progestagens, and androgens, respectively, are excreted annually by feedlot animals, and almost 90% of estrogens and progestagens and 40% of androgens are from cattle (Lange et al. 2002). Presumably in combination with endogenous compounds, synthetic steroids, such as trenbolone acetate and melengestrol acetate, may be metabolized and released into the environment only through cattle manure (liquid or solid). Natural and…

Current knowledge on the environmental fate, potential impact, and management of growth-promoting steroids used in the US beef cattle industry