Growth Promoting Steroids
The importance of the sex hormones, both androgens and oestrogens, in controlling fatness and growth is illustrated by the use of synthetic growth-promoting substances (anabolic steroids) based on them. Androgens have actions like the male sex hormone testosterone. Oestrogens have actions like the female sex hormone oestradiol. Progestagens act like the female hormone progesterone, the main physiological function of which is to suppress oestrus, and have been used to enhance the effects of the other sex hormones. Trenbolone acetate is a synthetic androgen that promotes growth by decreasing protein degradation in muscle. Similarly, the synthetic oestrogen zeranol also promotes growth by decreasing protein degradation. Both hormones therefore work by reducing protein turnover rather than by increasing protein synthesis. As might be expected, the effects of synthetic sex hormones depend to a degree on the sex of the animal to which they are administered since it is the balance of male and female hormones which is important. Females tend to respond better to androgens and males to oestrogens. Castrates tend to respond best to a combination of androgens and oestrogens. The use of anabolic sex steroids, usually as implants, was wide-
spread in cattle in Europe until banned in the EU (EU Directive 88/146/EEC). There was concern about the potential effects of steroid residues on humans who consumed the meat and offal from treated animals particularly if the recommended dose rates had not been adhered to. Nevertheless, the compounds are still in use in many countries outside the EU, including North America. Examples of anabolic sex hormone products are given in Table 2.10. Anabolic sex steroids are usually administered as compressed tablets implanted into
the tissues of the ear (a non-edible part of the animal). Other growth promoting steroids that have been used are the stilbenes (diethyl stilboestrol, hexoestrol) which were banned in the EU in 1981 and also North America, because of concerns, possibly unfounded, that they could cause cancer in people eating meat.
spread in cattle in Europe until banned in the EU (EU Directive 88/146/EEC). There was concern about the potential effects of steroid residues on humans who consumed the meat and offal from treated animals particularly if the recommended dose rates had not been adhered to. Nevertheless, the compounds are still in use in many countries outside the EU, including North America. Examples of anabolic sex hormone products are given in Table 2.10. Anabolic sex steroids are usually administered as compressed tablets implanted into
the tissues of the ear (a non-edible part of the animal). Other growth promoting steroids that have been used are the stilbenes (diethyl stilboestrol, hexoestrol) which were banned in the EU in 1981 and also North America, because of concerns, possibly unfounded, that they could cause cancer in people eating meat.
Nama Produk Hormon ProdusenFinaplix® Trenbolone acetate Hoechst
Ralgro® Zeranol Crown Cheodusmicals
Compudose® Oestradiol Elanco
Synovex S® Oestradiol + progesterone Syntex
Synovex H® Testosterone + oestradiol Syntex
Beta-Adrenergic agonists
A class of pharmacological compounds that has shown enormous potential to alter the muscularity and ratio of lean to fat in meat animals is the Beta-adrenergic agonists. These have chemical structures
similar to the naturally occurring catecholamines, adrenaline (epinephrine) and noradrenaline (norepinephrine). Adrenaline and noradrenaline are hormones that are secreted in response to stressful
situations (see Chapter 10). Noradrenaline is also the neurotransmitter found in the sympathetic nervous system (equivalent to the acetylcholine of the parasympathetic system). Examples of Beta-adrenergic agonists are clenbuterol, cimaterol, salbutamol and ractopamine.
Beta Adrenergic agonists are so called because they act on cells via Betareceptors on the cell membrane. The Beta receptors can be subdivided into two types. Beta 1 receptors are characteristic of cardiac and intestinal muscle; Beta 2 receptors are characteristic of bronchial and uterine smooth muscle. However, both Beta 1 and Beta 2 receptors occur in many tissues including skeletal muscle and fat. The Beta -adrenergic agonists of interest in animal production mainly affect Beta 2 receptors but the classification into Beta 1 and Beta 2 is not clear-cut and some Beta 1 activity is also evident. The potential value of Beta -adrenergic agonists in meat animals lies in their so-called repartitioning effects. They reduce the amount of fat in the body and increase protein accretion so promoting muscular development. They appear to do this by both reducing the production of fat (lipogenesis) and increasing fat breakdown (lipolysis; Cardoso and Stock, 1998). Their action on protein accretion seems to be through reducing breakdown, so favouring the synthesis component of the normal protein turnover. Some muscles, particularly those with a high proportion of type II, glycolytic, fast contracting fibres (see Chapter 3), are more affected than others. Although they influence circulating levels of insulin, growth hormone and the thyroid hormones, it is not thought that the effects of Beta-adrenergic agonists are mediated through these. Unlike anabolic steroid hormones, Beta-adrenergic agonists are effective in all sexes to the same extent. They are orally active and so can be administered in the feed, usually at levels of between 1 and 10 ppm. They are therefore effective at very low doses. Although they may show small effects on growth rate this is not a consistent effect and is generally more apparent in ruminants than in non-ruminants. Carcass yield is improved by around 1–2% in pigs and poultry and by up to 5–6% in cattle and sheep. There is evidence that this is due to both an increase in carcass weight and a decrease in the size of the viscera. The carcasses have better conformation. The increases in muscle development are accompanied by reductions in subcutaneous, intermuscular and intra-muscular fat. The effects of administration of a Beta-adrenergic agonist to pigs are illustrated in Table 2.11. A comparison of the effects of treatment with Beta-adrenergic agonists on pigs and sheep is shown in Table 2.12. These figures illustrate the potential gains to be had from administration of Beta-adrenergic agonists. However, the gains are offset by potentially poorer meat quality. Some Beta-adrenergic agonists may produce meat thatis darker and duller in colour, and tougher after cooking. The darker colour is caused by reduced glycogen levels in the muscles at slaughter leading to a higher ultimate pH in the muscles. Toughness may result from a lower activity of proteolytic enzyme systems post mortem (see Chapter 5). By reducing intramuscular fat, Beta-adrenergic agonists may also reduce other eating quality characteristics.
Ralgro® Zeranol Crown Cheodusmicals
Compudose® Oestradiol Elanco
Synovex S® Oestradiol + progesterone Syntex
Synovex H® Testosterone + oestradiol Syntex
Beta-Adrenergic agonists
A class of pharmacological compounds that has shown enormous potential to alter the muscularity and ratio of lean to fat in meat animals is the Beta-adrenergic agonists. These have chemical structures
similar to the naturally occurring catecholamines, adrenaline (epinephrine) and noradrenaline (norepinephrine). Adrenaline and noradrenaline are hormones that are secreted in response to stressful
situations (see Chapter 10). Noradrenaline is also the neurotransmitter found in the sympathetic nervous system (equivalent to the acetylcholine of the parasympathetic system). Examples of Beta-adrenergic agonists are clenbuterol, cimaterol, salbutamol and ractopamine.
Beta Adrenergic agonists are so called because they act on cells via Betareceptors on the cell membrane. The Beta receptors can be subdivided into two types. Beta 1 receptors are characteristic of cardiac and intestinal muscle; Beta 2 receptors are characteristic of bronchial and uterine smooth muscle. However, both Beta 1 and Beta 2 receptors occur in many tissues including skeletal muscle and fat. The Beta -adrenergic agonists of interest in animal production mainly affect Beta 2 receptors but the classification into Beta 1 and Beta 2 is not clear-cut and some Beta 1 activity is also evident. The potential value of Beta -adrenergic agonists in meat animals lies in their so-called repartitioning effects. They reduce the amount of fat in the body and increase protein accretion so promoting muscular development. They appear to do this by both reducing the production of fat (lipogenesis) and increasing fat breakdown (lipolysis; Cardoso and Stock, 1998). Their action on protein accretion seems to be through reducing breakdown, so favouring the synthesis component of the normal protein turnover. Some muscles, particularly those with a high proportion of type II, glycolytic, fast contracting fibres (see Chapter 3), are more affected than others. Although they influence circulating levels of insulin, growth hormone and the thyroid hormones, it is not thought that the effects of Beta-adrenergic agonists are mediated through these. Unlike anabolic steroid hormones, Beta-adrenergic agonists are effective in all sexes to the same extent. They are orally active and so can be administered in the feed, usually at levels of between 1 and 10 ppm. They are therefore effective at very low doses. Although they may show small effects on growth rate this is not a consistent effect and is generally more apparent in ruminants than in non-ruminants. Carcass yield is improved by around 1–2% in pigs and poultry and by up to 5–6% in cattle and sheep. There is evidence that this is due to both an increase in carcass weight and a decrease in the size of the viscera. The carcasses have better conformation. The increases in muscle development are accompanied by reductions in subcutaneous, intermuscular and intra-muscular fat. The effects of administration of a Beta-adrenergic agonist to pigs are illustrated in Table 2.11. A comparison of the effects of treatment with Beta-adrenergic agonists on pigs and sheep is shown in Table 2.12. These figures illustrate the potential gains to be had from administration of Beta-adrenergic agonists. However, the gains are offset by potentially poorer meat quality. Some Beta-adrenergic agonists may produce meat thatis darker and duller in colour, and tougher after cooking. The darker colour is caused by reduced glycogen levels in the muscles at slaughter leading to a higher ultimate pH in the muscles. Toughness may result from a lower activity of proteolytic enzyme systems post mortem (see Chapter 5). By reducing intramuscular fat, Beta-adrenergic agonists may also reduce other eating quality characteristics.
