Steroids are a class of organic compounds found naturally in animals and plants, characterized by a distinct molecular structure composed of four fused carbon rings. These compounds function primarily as signaling molecules, acting as hormones that regulate a vast array of physiological processes within the body. In veterinary science and animal production, synthetic versions of these hormones are utilized to manage health conditions or to influence growth and metabolism.
Two Main Categories of Steroids Used in Animals
The term “steroid” encompasses two major categories with fundamentally different effects: anabolic steroids and corticosteroids. Anabolic steroids are synthetic derivatives of the male sex hormone testosterone, designed to maximize the anabolic (tissue-building) effect while minimizing the androgenic (male-characteristic promoting) effect. They function by binding to androgen receptors inside muscle and bone cells, which stimulates protein synthesis and reduces protein breakdown, leading to increased muscle mass and strength.
Corticosteroids are synthetic versions of hormones produced by the adrenal glands, such as cortisol. Their primary mechanisms of action involve modulating the immune system and regulating metabolism. Specifically, glucocorticoids—the most commonly used type—reduce inflammation and suppress immune responses by inhibiting the release of inflammatory chemicals.
Therapeutic Applications in Veterinary Medicine
Corticosteroids, particularly glucocorticoids, are widely prescribed in veterinary medicine due to their powerful anti-inflammatory and immunosuppressive properties. They are frequently used to manage allergic reactions in companion animals, such as severe skin inflammation or chronic allergic bronchitis. They also play a role in treating autoimmune disorders, where they suppress the immune system’s attack on the body’s own tissues, as seen in certain types of immune-mediated arthritis.
Anabolic steroids have limited, specific therapeutic applications, primarily to reverse severe muscle wasting. They may be prescribed for an animal suffering from a debilitating condition, chronic infection, or following major surgery to restore a positive nitrogen balance. By promoting protein synthesis, these compounds help counteract the catabolic state—the breakdown of muscle tissue—often caused by long-term illness or the side effects of other drugs, including high doses of corticosteroids.
Steroids for Growth Promotion in Livestock
The non-therapeutic application of steroids is most prominent in the livestock industry, specifically for growth promotion in beef cattle. In the United States, hormonal implants containing natural steroids like estradiol, progesterone, and testosterone, along with synthetic compounds, are approved for use. These implants are small pellets placed under the skin of the animal’s ear, where they release a controlled dose over time.
The goal of this practice is to increase the rate of weight gain and improve feed efficiency—the amount of weight gained per unit of feed consumed. The use of these implants can increase an animal’s average daily gain by approximately 15% to 25% and improve feed efficiency by about 5% to 15%. This effect is achieved because the anabolic hormones stimulate the production of insulin-like growth factor-1 (IGF-I) and bind to muscle cell receptors, resulting in greater protein deposition.
Regulatory approaches differ significantly across global markets for this application. While the U.S. permits the use of specific hormonal implants under strict federal oversight, the European Union (E.U.) has enforced a comprehensive ban on the use of all six growth-promoting hormones in livestock since 1988. This prohibition also extends to the importation of meat from animals treated with these substances.
Regulatory Oversight and Consumer Safety
Government agencies, such as the U.S. Food and Drug Administration (FDA) and the Department of Agriculture (USDA), regulate the use of all drugs, including steroids, in food-producing animals to ensure consumer safety. A core element of this oversight is establishing a tolerance, which is the maximum concentration of a drug residue legally permitted in edible animal tissue. This tolerance is set at a level that is determined to be safe for human consumption.
For approved steroid implants used for growth promotion, the FDA often assigns a “zero-day withdrawal period.” This means that the hormones are metabolized by the animal quickly enough, and the resulting residue levels in the meat are so low, that the food product is considered safe at any time after treatment. Furthermore, the ear—where the implant is placed—is discarded during processing and does not enter the human food supply.
Producers must strictly follow the drug label instructions, as using a drug in a way not specified on the label, known as extra-label use, is illegal and can lead to unacceptable residue levels. Federal agencies also perform residue testing on meat products to monitor compliance with established tolerance levels. This regulatory framework is designed to minimize any potential human exposure to drug residues through the food chain.