Recycling and degradation of anabolic agents in animal excreta

A variety of anabolic agents are currently added to animal feeds to increase growth rate and improve feed efficiency. These compounds and their metabolites are largely excreted. Prior to the use of anabolic agents as feed additives and the advent of confined livestock production, natural recycling occurred which generally resulted in benefit to the animal with no known adverse effects on consumer health. However, the current interest in the use of animal excreta in livestock feed and the possible presence of anabolic agents and their metabolites from this practice has created an additional need for information on the occurrence of anabolic agent residues in consumer products. This report will consider the definition of anabolic agents in its broadest sense and discuss the research on hormones used in animal feed that may be found in animal excreta. In addition to feed additive residues, endogenous compounds may also be found in animal excreta. Endogenous estrogens and androgens have been detected in excreta from domestic livestock and poultry. Research results suggest that substantial estrogenic and androgenic activity may be detected in fresh animal excreta. However, little is known about the effects of various processing methods of excreta such as heat drying and fermentation on its hormonal activity. The effects of feed additive residues and endogenous hormones in excreta used for feed will be discussed relative to their impact on animal health and occurrence in animal products.