Heitzman R J
Environ Qual Saf Suppl. 1976(5):89-98.
In many countries anabolic agents are successfully used to increase the rate of growth of cattle. In the past widespread use was made of cheap synthetic estrogens such as diethylstilbestrol and hexestrol. However, new legislation in certain countries has restricted the use of synthetic estrogens. This has resulted in an intensive search by industry for alternative agents. On the one hand natural steroid hormones like estradiol, testosterone and progesterone were studied, while on the other hand products like an active compound of the resorcyclic acid lactones and the synthetic anabolic steroid trenbolone acetate were developed. Administration of anabolic agents to cattle is done in three ways. (1) The agent may be fed orally by incorporation into the concentrate feed or as a simple additive top dressing. If the agent is metabolised in the rumen, oral administration may still be possible by using coated materials which avoid rumen metabolism with subsequent absorption of the steroid from the small intestine. (2) The agent may be administered as a slow release implant, e.g. trenbolone acetate or various combined preparations of an androgen and estrogen. (3) Administration by repeated injection. This latter method is often impractical. Anabolic agents are normally administered to beef cattle or culled dairy cows during the last few months of the finishing period. Maximum weight gain performance in different types of cattle requires selection of the correct anabolic agent. Increased performance in female cattle is better when an androgenic steroid is administered. However, in intact males (bulls) best performance is only obtained when an estrogen, alone or in combination with an androgen, is administered. Castrate animals (steers) do best if a smaller amount of estrogen is combined with an androgen and administered, however there is evidence that androgen alone is as effective. In summary therefore, an additional response in growth of cattle may require the presence of an estrogen, as endogenous estrogen in the female and the exogenous form in the male. Only when this condition is met will administration of androgenic anabolic steroids result in maximum benefit, often improving the effect of estrogen given on its own. Anabolic agents have some beneficial effect on appetite. They may not affect the digestive processes of the alimentary system. They have a positive effect on nitrogen retention. The liver almost certainly has a central role in the regulation of nitrogen retention. Recent experiments suggest that urea entry rates in ruminants may be lowered, thus making available more nitrogen for protein synthesis. Muscle protein synthesis is altered with changes in carcass conformation. There are some changes in fat redistribution. How all these processes are integrated is not yet known. The possibility that anabolic agents establish a new hormonal status which is favourable to growth will be discussed...
在许多国家，合成代谢剂被成功用于提高牛的生长速度。过去，人们广泛使用廉价的合成雌激素，如己烯雌酚和己烷雌酚。然而，某些国家的新立法限制了合成雌激素的使用。这导致行业内密集寻找替代剂。一方面，研究了天然类固醇激素，如雌二醇、睾酮和孕酮，另一方面，开发了如间苯二酚酸内酯的活性化合物和合成合成代谢类固醇醋酸群勃龙等产品。给牛施用合成代谢剂有三种方式。(1) 可通过掺入浓缩饲料或作为简单添加剂进行表层施肥口服施用该剂。如果该剂在瘤胃中代谢，通过使用避免瘤胃代谢并随后从小肠吸收类固醇的包衣材料，口服施用仍可能可行。(2) 该剂可作为缓释植入剂施用，例如醋酸群勃龙或雄激素和雌激素的各种联合制剂。(3) 通过重复注射施用。后一种方法通常不切实际。合成代谢剂通常在育肥期的最后几个月施用于肉牛或淘汰的奶牛。不同类型的牛要实现最大增重性能，需要选择正确的合成代谢剂。给雌性牛施用雄激素类固醇时，其性能提升更好。然而，对于未阉割的雄性（公牛），只有单独或与雄激素联合施用雌激素时，才能获得最佳性能。去势动物（阉牛）如果将较少量的雌激素与雄激素联合施用效果最佳，不过有证据表明单独使用雄激素同样有效。因此，总的来说，牛生长的额外反应可能需要雌激素的存在，雌性中的内源性雌激素和雄性中的外源性雌激素。只有满足这一条件，施用雄激素合成代谢类固醇才会带来最大益处，通常会增强单独施用雌激素的效果。合成代谢剂对食欲有一些有益影响。它们可能不会影响消化系统的消化过程。它们对氮保留有积极作用。肝脏几乎肯定在氮保留的调节中起核心作用。最近的实验表明，反刍动物的尿素进入率可能会降低，从而为蛋白质合成提供更多氮。随着胴体形态的变化，肌肉蛋白质合成也会改变。脂肪重新分布也有一些变化。所有这些过程是如何整合的尚不清楚。将讨论合成代谢剂建立有利于生长的新激素状态的可能性……
