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Encyclopedia Of Animal Science - H

Từ điển khoa học động vật vần H | Hormones Anabolic Agents Hugh Galbraith University of Aberdeen Aberdeen U.K. INTRODUCTION Growth in animals is well known to be influenced by a range of endogenous anabolic compounds that promote commercially desirable greater lean tissue deposition and reduced fat in body tissues. These compounds which act directly or indirectly to alter anabolic or catabolic processes include protein hormones and growth factors and steroidal androgens and estrogens. Of these only androgenic and estrogenic compounds along with certain progestagens have been approved for commercial application in farm animals. This long-standing practice now mainly applies to beef production in North American countries. In contrast the European Union has applied the precautionary principle and prohibited both the use of these preparations internally and importation of meat from treated animals from external countries. This prohibition is frequently questioned on the grounds of the small amounts of residues consumed in beef in relation to endogenous quantities in humans and those determined as safe by toxicological methodology. This review will consider for the anabolic agents in commercial use application and responses in practice mode of action residues and contemporary issues relating to risk assessment for human consumers and the general environment. APPLICATION PROPERTIES AND CONSUMER ISSUES Commercial Preparations Hormone Delivery Responses and Mode of Action The anabolic preparations available in the United States 1 contain naturally occurring testosterone T and its propionate ester estradiol-17p E and its benzoate ester progesterone Pr and the xenobiotic compounds trenbolone acetate TA zeranol Z and melengestrol acetate MGA . Active ingredients may be further characterized as estrogens E is a steroid hormone synthesized mainly in gonadal tissues Z is a resorcylic acid lactone derivative of the nonsteroidal fungal estrogen zearalenone steroidal androgens T is a hormone synthesized in gonads .