By: Erica Larson
Anything found naturally in a horse’s body is allowed to be there on a drug test, right? Not necessarily.
Cobalt, for example, is a trace mineral found in B vitamins that horses require in tiny amounts for their bodies to function correctly. As a result, all horses have trace amounts of the substance in their systems. But when tests reveal higher doses of cobalt—after a larger dose of the substance is administered, for instance—it often means a trainer or handler attempted to gain a competitive advantage. This is considered doping.
To confound things, researchers don’t yet understand how high a cobalt dose must be to affect a horse’s body—just that it could be putting both horses and their handlers at risk. At the 2016 American College of Veterinary Internal Medicine Forum, held June 8-11 in Denver, Colorado, Teresa Burns, DVM, PhD, Dipl. ACVIM, an assistant clinical professor of equine internal medicine at the Ohio State University College of Veterinary Medicine, in Columbus, shared study findings on the topic.
Human doctors used cobalt to treat anemia (essentially by increasing erythropoiesis and, therefore, the blood’s oxygen-carrying capacity) in humans for decades. However, it was associated with a variety of adverse effects, including gastrointestinal, neurologic, cardiovascular, and thyroid problems. As a result, doctors have largely ceased using it. Some athletes, however, continue using it as a doping agent, as an increased oxygen carrying capacity is thought to improve an athlete’s aerobic capacity and endurance.
In the past few years, that same trend appears to have spread into the world of horse racing: “Cobalt is reportedly given to racehorses to enhance performance,” Burns said.
One of the key problems with this is that veterinarians still aren’t entirely sure how cobalt affects the horse’s body.
“While preliminary single-dose pharmacokinetic data have been published for cobalt in horses, information regarding the effects of repeated dosing—which is how the substance is reportedly used illicitly in performance horses—is unavailable,” Burns said. “Even fewer data have been published describing the pharmacodynamic effects of cobalt in horses, particularly at high doses.”
As such, Burns and colleagues set out to describe the effects of weekly intravenous (IV) cobalt administration.
The team employed five Standardbred mares, each of which received one of five cobalt doses (0.25, 0.5, 1, 2, or 5 mg/kg body weight) weekly for five weeks. They assessed a number of parameters every five to 10 minutes for four hours after administering the first and fifth weekly doses. The cobalt was administered in a rapid IV infusion over one minute.
Key findings included:
- Subjectively, the researchers observed that all the mares showed signs of being anxious—nostril flaring, muscle fasciculation (twitching), pawing, and straining—by five minutes after administration; in mares that received 1, 2, or 4 mg/kg doses, the anxious behaviors persisted for about an hour following infusion;
- Mares receiving 1, 2, or 4 mg/kg doses developed a rapid heartbeat (ranging from 60 to 126 beats per minute; for comparison, the heart rate for an average adult horse typically ranges from 28 to 44 beats per minute) immediately after administration; mares receiving the lower doses did not experience this extremely rapid heart rate;
- The mare receiving the 4 mg/kg dose developed paroxysmal ventricular tachycardia (more on this in a moment) in the first 10 minutes following administration;
- All mares became hypertensive (developed high blood pressure) in the 30 to 45 minutes following infusion, the 4 mg/kg mare “profoundly” so, Burns said;
- Mares receiving 2 and 4 mg/kg doses developed congestion (blood accumulation) in their gums for about 20 minutes following administration before it resolved; and
- At all doses, cardiovascular abnormalities returned to normal approximately one hour following administration.
“The results from this preliminary study document significant, repeatable hemodynamic alterations associated with intravenous cobalt administration to horses,” Burns concluded. “There is no known therapeutic use of cobalt administered in this manner to horses; further, the degree of hypertension observed following infusion raises humane and human safety concerns if doses of more than 1 mg/kg are used.”
Specifically, she said, the degree of hypertension the mares developed could potentially result in serious complications, including large vessel rupture; hemorrhage; and acute, severe injury or death.
“Further,” she said, “the arrhythmia that mares receiving the highest doses developed (ventricular tachycardia) has been associated with a relatively high risk of acute cardiac death.”
The impulses that initiate each normal heartbeat arise from the sinoatrial node in more “garden-variety tachycardia,” Burns explained. “In ventricular tachycardia, the stimulus driving the tachycardia is somewhere lower down within the ventricular muscle. Usually some bit of cardiac tissue has been damaged in some way. Ventricular tachycardias are usually fast and can degenerate quickly to ventricular fibrillation and arrest. It’s a more dangerous rhythm, certainly.”
So what effects could these alterations, if a horse receives high doses of cobalt over time, have on the animal? And would an affected horse be safe as a riding horse following his racing career?
“We truly have no idea what chronic cobalt administration does in horses, as the studies to answer this question simply haven’t been done,” Burns explained. “Most of the literature published on cobalt in horses has addressed single-dose pharmacokinetics, which looks to answer the question ‘where does this drug go when given to a horse, and how (and how quickly) is it eliminated?’ We don’t know what performance benefit there might be with chronic cobalt administration in horses, and we don’t know what chronic cobalt toxicity looks like in horses.
“That said, it is fairly toxic in other species (humans and rodents), causing various nerve and endocrine disorders—we assume that it may have similar effects in horses, but we don’t know that with certainty. More work to be done!”
Along those lines, Burns said studies are underway in which researchers are hoping to identify acute cobalt administration’s performance-enhancing effects in racehorses (essentially, does it make them run faster and fatigue later?) and better understand the impact of short-term multi-dose cobalt administration on endocrine and other organ function.
“I think the ‘gut feeling’ from our research group is that cobalt chloride has the potential to be quite harmful to horses,” she relayed. “There is no known valid therapeutic use for this substance in equine veterinary medicine, and it is therefore an abuse of these animals to give it in an attempt to simply achieve a performance benefit.”