The growth of animals can be defined as an increase in mass of whole body, tissue(s), organ(s), or cell(s) with time. Improved understanding of the control of metabolic aspects of growth has provided the opportunity to regulate animal growth. Improvement of rate and efficiency of growth benefits the producer. Improvement in composition of meat animals benefits the producer through more efficient gain and greater value, and benefits the processor through less labor requirement for trimming and removal of fat. The consumer benefits by receiving a quality, desirable food at a cost reflective of efficient production.
Four general classes of growth regulators are approved by the Food and Drug Administration (FDA) for use in food‐producing animals in the United States. These include naturally occurring and synthetic estrogens and androgens, ie, anabolic steroids; ionophores; antibiotics; and bovine somatotropin. Compounds in the first class, anabolic steroids, act as metabolism modifiers to alter nutrient partitioning toward greater rates of protein synthesis and deposition, thereby increasing the weight at which 25 to 30% lipid content in the body or carcass is achieved. Ionophores have highly selective antibiotic activity and appear to enhance feed conversion efficiency through effects on ruminal microbes. Antibiotics, administered at subtherapeutic doses, enhance growth through improving feed conversion efficiency and/or growth rate, with no consistent effect on body or carcass composition.
Two other classes of growth regulators, ie, somatotropin or somatotropin secretogogues, and select synthetic phenethanolamines, have been investigated for the ability to alter growth; no compound in either class has yet been approved by the FDA for use in animals raised for meat. In 1993, the FDA approved administration of recombinant bovine somatotropin for increasing milk production in dairy cows.
The U.S. Food and Drug Administration's Center for Veterinary Medicine thoroughly evaluates the proposed use of any compound, natural or synthetic, used in food‐producing animals for human food safety, safety to the animal of intended use, and safety to the environment.