The Federal Food, Drug and Cosmetic Act governs FDA approval of implants. New animal drugs must be demonstrated to be safe and effective for their intended use. Safety must be demonstrated in food from treated animals being consumed by humans, in the health of the treated animal, in the environment at the time of manufacture and use in the animal, and in the human user of the product in animals. Human food safety considerations include drug residues that might occur in meat, milk and eggs. In the case of growth promoting implants, this only concerns meat since the implants are not approved in dairy cattle or poultry. Since the mid-1950s several generations of Americans have consumed beef from implanted animals with no adverse health effects.
Placement of implants
Implants are placed under the skin of the posterior aspect of the middle third of the ear of cattle. They remain in this site during the period that they secrete growth-stimulating hormones in extremely small amounts. Any remaining implanted materials, including the carrier matrix and the hormone compounds, are removed at slaughter and processing when the skin and ears are removed. This prevents human consumption of implant carrier matrix materials or hormone residues. The FDA places no slaughter withdrawal time restriction on the use of implants in cattle, meaning they may be treated and then immediately harvested because the meat will not have violative residues.
For an implant to be approved in a food-producing animal in the United States, the no-hormonal-effect level must be determined in the most sensitive experimental animal under well-controlled scientific studies. A safety factor of 100 is divided into the no-hormone-effect level to establish an “acceptable daily intake” (ADI) per unit of body weight for humans. The potential daily intake (PDI) is determined by multiplying the human average daily intake of animal tissues by any residue found in them after implanting. To be approved, PDI may not exceed ADI. Wide safety margins between ADI and PDI exist for all approved implants. For example, using the highest residue levels reported, a person consuming 1.1 pounds of beef from implanted cattle would consume an extra 30 to 50 nanograms of estradiol per day. The PDI for a 132-pound person is 100 times this amount (3,000 ng/day). Viewed another way, for a person to reach the PDI, he/she would have to consume 50 to 66 pounds of implanted beef per day containing the highest residue level reported.
Tissue residue allowance
Safe tissue levels have been determined for natural and synthetic hormones used in growth promotants. For implants using naturally occurring hormones, the maximum allowable levels are six to 15 times greater than the highest residues found in treated cattle. As an added safety measure, the FDA maximum safe tissue residue allowed for synthetic hormones is 77 and 150 times greater (trenbolone and zeranol, respectively) than levels detected in treated cattle.
Endogenous hormone level
Because human tissues and organ systems produce and require hormones as part of their physiological life processes, many of them are normally present in the human body in varying amounts. These include steroid hormones of the same type as those used in implants. The human body’s natural production of these hormones substantially exceeds the PDI from beef treated with implants.
Multiple assays designed to assess damage to DNA that can lead to mutations have been used to evaluate growth promotants. All of these assays have been negative. At extremely high doses, some studies with rodents have reported increased tumor development; however, no studies have reported the same results with higher order mammals. Humans metabolize hormones differently than rodents, which may explain why the carcinogenic link found in rats has not been duplicated in humans.
Steroid use in athletes
Some athletes have used anabolic and androgenic steroids to increase performance. Negative effects of their abuse are well known to the general public. The dosage taken by athletes, called supraphysiologic, is 10 to 100 times the rate used in hormone replacement therapy, and is most often injected, which increases the potency of the hormone. Athletes illegally taking steroids will inject 600 to 1,000 milligrams per week of testosterone, compared with the highest dosage in treated cattle of 200 milligrams, which is released over a much longer period of time (100 to 120 days). The amount of hormone injected by athletes results in a dose seven to 10 times that produced by the testes of normal men. The misuse of steroids by humans is not to be confused with proper use in food-producing animals.
The European Union does not permit the import of U.S. beef because of the approved use of implanting technologies in the U.S. Nonetheless, the European Agriculture Commission convened a scientific conference on growth promotion in meat production in 1995 that concluded that on the basis of the “data available, it seems most unlikely or even impossible that the residues following the use of these compounds according to good agriculture practice will ever exceed the set tolerance levels.” In addition to the United States, approximately 30 countries have approved growth-promoting implants for use in cattle. Paradoxically, in those countries where implants are banned, there is evidence that potentially harmful growth-promoting compounds are being used in an illegal fashion to a large and unregulated extent in cattle.
Impact on animal welfare
Minor behavioral changes in treated cattle have been reported. However, incidence of these events has been low, related to improper implanting procedures and has been difficult to repeat in controlled studies.
Read more: Part 2: Growth-Promoting Hormones