Q. My horse had a soft tissue injury and my veterinarian gave him steroids. Some of the people in my barn say I need to be careful that he doesn’t get too aggressive or get foundered. I’m confused. How can steroids do all of that?

A. The steroids, an extremely broad category of drugs and natural hormones, have a wide variety of effects on the body. All drugs when used for the wrong reasons or at an inappropriate dose or frequency of treatment can be toxic--the steroids are no exception.

The two main classifications of steroids are the anabolics and the corticosteroids (the reproductive hormones such as estrogen, progesterone, and others are also classified as "steroids"). The anabolic steroids function to increase protein synthesis by the body and build muscle mass. The drugs are designed to be used in the treatment and rehabilitation of chronic debilitating disease processes. The drugs often are used in attempting to make a gelding act more like a stallion and to promote the development of muscle mass and therefore strength, stamina, and endurance. The drugs allow for a better conversion of the protein ingested through feed into body proteins (and more particularly muscle tissue).

The anabolic steroids should be used with caution and within ethical boundaries. There can be severe side effects that include making a horse so hyped-up that he actually becomes dangerous to humans. There also is the development of liver disease with chronic use. The anabolic steroids have pharmaceutical actions on the body that are very different from the corticosteroids.

Some corticosteroids only have an effect for 30-40 minutes after administration, whereas others can have an effect for weeks. The individual potency also varies greatly, with some being 100 to 1,000 times more powerful than others.

One of the major mechanisms of action of the corticosteroids is to decrease inflammation. The corticosteroids also reduce inflammation associated with allergic reactions--one important use is for the treatment of allergic airway disease (allergic bronchitis or chronic obstructive pulmonary disease--COPD or heaves).

The corticosteroids are extremely potent anti-inflammatory agents that also are useful in the treatment of numerous disease processes. The most common usage is for the treatment of arthritic conditions and certain types of joint problems.

As with all drugs, there are a good side and a bad side. The good side is that the corticosteroids are very effective in reducing the inflammation associated with joint injury and arthritis. The bad side is that they potentially can have a seriously negative impact on cartilage health. Corticosteroids, if used inappropriately, can destroy the cartilage and potentially contribute to chronic arthritis.

The corticosteroids have a well-documented negative impact on normal healing with respect to soft tissue (tendon and ligament) injury. So, essentially any injury where corticosteroids are used will have a delay in the healing process. The corticosteroids often are injected locally or applied topically with "carrier" agents such as DMSO to the areas of soft-tissue injury. Again, this has a good and a bad side. The decrease of inflammation in soft tissue injuries is very important for the overall outcome. But in some cases, if the horse continues working in the face of that injury, more serious tendon or ligament damage can occur. The horse is working on an injury that feels better due to the steroids, so not only is he placing normal strains on injured tissue, that tissue’s healing responses have been decreased.

It has been well demonstrated that long-term chronic use of systemic steroids (especially at higher doses) suppresses the immune system. In competition horses already experiencing stresses that can supress the immune system (e.g., trailering), these effects might be compounded. Horses given corticosteroids on a regular basis might be predisposed to chronic infection--lung and sinus most commonly.

Another side effect of corticosteroids in the horse is laminitis or founder. The specific reason why corticosteroids predispose to founder is unknown, but it is thought to be related to an effect on the blood supply to the deep layers of the foot. The occurrence of this phenomenon is variable and is more likely to occur when more potent types of corticosteroids are used or very high doses of the less potent ones are used for long periods of time.

The exception to this is the individual horse, which for unknown reasons, is more sensitive to corticosteroids with respect to founder. It has been observed that even a few low doses of less-potent corticosteroids will cause sore feet in some horses.

In addition, if systemic corticosteroids are used, an effort should be made to 1) use as low a dose as possible to achieve the desired therapeutic effect; 2) use them for as short a time period as possible; 3) monitor the horse for any signs of development of infection, e.g., daily temperature taken while on the drug; and 4) monitor the horse for any signs of laminitis or founder (sore feet/lameness, warm feet, etc.). Also, it should be remembered that if the corticosteroids are being given for a musculoskeletal problem, a significant masking of pain can occur. Continued exercise of injured tissue might not be in the best interest of the horse.

The use of either corticosteroids or anabolic steroids should only be under the advice and prescription of a veterinarian.

About the Author

Michael Ball, DVM

Michael A. Ball, DVM, completed an internship in medicine and surgery and an internship in anesthesia at the University of Georgia in 1994, a residency in internal medicine, and graduate work in pharmacology at Cornell University in 1997, and was on staff at Cornell before starting Early Winter Equine Medicine & Surgery located in Ithaca, N.Y. He is also an FEI veterinarian and works internationally with the United States Equestrian Team.

Ball authored Understanding The Equine Eye, Understanding Basic Horse Care, and Understanding Equine First Aid, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.

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