Growth promoters are mainly used in farm animals with the purpose to promote growth, to improve the distribution of fat and protein, and to increase the feed-to-muscle conversion rate. Growth promoters mainly include hormones, beta-agonists, and antibiotics. Most growth promoters are orally active and can be administered either in the feed or in the drinking water, while other active hormones can be administered in the form of small implants into the subcutaneous tissue of the ears. This allows for slow release that may last for several weeks or even months. However, some residues may remain in the tissues of the treated animals several days after their administration at toxicologically unacceptable concentrations that may cause health issues to consumers. Such as β-agonists cause certain phenomena like gross tremors of the extremities, tachycardia, nausea, headaches, and dizziness. This makes it necessary to provide accurate control rules and inspection services and analytic methodologies for safety assurance purposes.
Hormones are endogenous biochemical messengers which are transported through the bloodstream to their target organs. These compounds are used in the production of food animals to promote growth and increase the efficiency of feed utilization. In the case of bovine somatotropin, it increases milk production. However, the use of hormones in such animals has provoked many concerns on human health impacts. A better understanding of health risks posed by the use of such drugs is essential for making proper regulatory decisions and programmers that support the prudent nonhuman use of hormonal drugs. The EU has prohibited the use of substances having a hormonal action for growth promotion in farm animals. Examples for these kinds of growth promoters are oestradiol 17ß, testosterone, progesterone, zeranol, trenbolone acetate and melengestrol acetate (MGA).
β-Agonists are synthetic derivatives with similar chemical structures of the naturally occurring catecholamines. They are used as medication for the treatment of respiratory diseases such as asthma. Beta-agonists facilitate the use of fats rather than glucose as a fuel source. This improves the meat: fat ratio of animals and leads to the production of higher quality meat at lower cost. When animals are treated with ß-agonists, drug residues may remain in the animal's meat and milk, which may be harmful to the consumer. The use of Beta-agonists as growth promoters has been banned in most countries. Consequently, it is important that abuse of these compounds is monitored.
Antibiotics used as feed additives, develop their activity in the digestive tract of animals by suppressing the undesired competitive microorganisms that utilize nutrients and produce undesirable or toxic substances resulting in an optimal environment for the intestinal mucosa. Therefore, it allows efficient nutrient absorption, and increases nutrient utilization as well as feed conversion.
Figure 2. Proposed modes of action of antibiotics as growth promoters
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