During the course of fifty years, anabolic steroids have become well renowned for their safe and effective growth-promoting activities that work in improving muscle leanness, augmenting the daily average gain, the moderate stimulation of the feed intake, and consequently improving the feed efficiency, which is the gain rate in relation to the quantity of feed required to attain such gain. It is therefore unsurprisingly common that over ninety percent of the total feedlot cattle in the United States alone have received some sort of steroidal implant throughout their lifetime. (NAHMS, USDA 2000)
Anabolic agents may be administered into the cattle via one of the two most common routes; the first being an oral intake where the agent is integrated into the concentrate feed, such as the newly FDA approved Beta agonists that pref¬erentially works at increasing carcass lean tissue by the end of feeding period. While the second route pertains to the use of subcutaneous slow releasing implants containing trenbolone acetate (testosterone analogue) or combined preparations of androgens and estrogens, where TBA/E2 implants are the most prominently used (Heitzman,1976). Generally, such implants have been shown to increase the growth rate from 8% to 28%, improve feed effi¬ciency by 15% and enhance carcass lean tissue mass from 3 to 10 percent. (Duckett and Owens, 1997).
Such enhancements have generated remarkable production benefits for the beef industry, especially in productiv¬ity, which is the amount of beef produced per animal.
Therefore benefits arising from feed efficiency improvements starts by a drastic decrease in production costs by lessening the quantity of food supply needed per unit of gain. Furthermore, consumers would still obtain the same amount of food even though less land is being used. Greenhouse gases production would become restrained when the amount of animals needed to produce the same quantity of beef is reduced. (Avery and Avery, 2007) Moreover, another added benefit for improving feed efficiency is through providing consumers an affordable beef supply at lower costs. (Lawrence and Ibarburu, 2009).
One of the main advantages for steroidal implant use is the improvement of protein accumulation (lean tissue deposits) within the carcass. Therefore, retail product cost per head may be increased up to $100 due to the improvements in lean tissue deposition (Hancock et al., 1991). Moreover, since the growth composition of meat is modified and altered more towards lean tissue than for adipose tissue, a much healthier nutrient-rich product with subsequently less calories is produced.
Since animal products contribute significantly to the total caloric and nutri¬ent intake in the human population, altering the composition of growth toward more lean tissue and less adipose tissue results in a healthier product with fewer calories that still is rich in benefi¬cial nutrients.
The New Animal Drug Application (NADA) process are responsible for testing the majority of growth-promoting com¬pounds before finally being approved off and mandated by the FDA. Such procedures are quite methodical and systemic; therefore they are managed and supervised by scientists at the FDA’s Office of New Animal Drug Evaluation within the Center for Veterinary Medicine (CVM). The authorization of a new growth –promoting drug is granted, only if a standard 75 independent studies that document certain health safety regulations such as human food safety, animal safety, efficacy, environmental safety, and user safety, are met.
The classification of compounds:
Estrogens, androgens, and progestins are of the widely used anabolic steroids that can be either naturally occurring or synthetic. The natural hormones are found in all mam¬malian species regardless of gender. Whereas the three most commonly used synthetic compounds in beef cattle production are zeranol, trenbolone acetate,and melegestrol acetate, with the resultant growth rate and feed ef¬ficiency enhancement..
Zeranol, a nonsteroidal macrolide and is a naturally occurring ?-resorcyclic acid lactone, which was initially isolated from corn mold. Even though a non-steroid by nature, it has yet maintained in demonstrating estrogen-like biological behaviors in cattle.
Trenbolone acetate (TBA) (1967), is a testosterone analogue with 10 to 50 times the anabolic activity of testos¬terone (Bouffault ; Willemart, 1983). It is often used in combination with an estrogen (mainly E2) to maximize growth rate and efficiency in cattle, especially in steers. During 2008, nearly two-thirds of all implants marketed in the U.S. were estimated to be single implants of different TBA and E2 (TBA/E2) concentrations. Therefore, TBA and E2 at var¬ious concentration levels remain the most widely used type of growth-promoting implants in the industry.
Melengestrol acetate (MGA) is accepted for the use in feedlot heifers for estrus suppression and growth efficiency enhancement. Although an exogenous, synthetic progestin, however melengestrole acetate with its unique characteristics would al¬low it to become active once fed to heifers at 0.40 mg/head/day, therefore it highly unnecessary to administer this compound as an implant. Cattle producers can safely feed this product until harvest, due to its rapid metabolism by the animal, with no