Potential dangers of rHuEPO
"The horse has some protective mechanisms, but when we did our studies, we had a cutoff point for administering the rHuEPO,"
states McKeever. "We were worried about getting the blood too thick."
Thickening the blood could result in clotting, a reduction in cardiac output and the ability to transport oxygen since the
horse is naturally losing fluids at exercise. Add the diuretic furosemide, which is commonly administered in racing horses,
and you may exacerbate the problems.
"Not only do you have the cross-reactivity problem, but if the blood becomes too viscous, and you don't know where that occurs
in the horse, you could potentially run into sludging problems—microvascular problems that could disrupt the function of very
small vessels," McKeever says. "That is what they purportedly see in humans. With the thickening of fluid within small vessels
and an increase in red blood cells, one may begin to develop blood clots. Then add the use of furosemide or aminocaproic acid,
and you're asking for a disaster."
Despite rHuEPO's purported benefit, the horse's physiology remains extremely sensitive, fighting to maintain blood pressure,
blood volume and blood tonicity.
"When we administered rHuEPO (as in some human studies), producing a short-term increase in red cell mass and blood volume,
the body sensed that via its baroreceptors and signaled to get rid of some of that extra blood volume," McKeever says. "We
actually saw a decrease in plasma volume. Therefore, although you've increased the red cell mass, you've maintained overall
blood volume at the expense of plasma volume. This could have implications for normal regulation, since you no longer have
the pool of water for sweat production."
In addition to rHuEPO, there are other hematinics that are available, as companies are working on other ways to stimulate
red cell production, and there are numerous products that purport to increase red cell mass.
"If they work, they fall into the same nefarious category as rHuEPO," McKeever says. "If they don't work, then people are
wasting money on useless, unethical products, despite their purported benefit."
Ed Kane, PhD, is a researcher and consultant in animal nutrition. He is an author and editor on nutrition, physiology and
veterinary medicine with a background in horses, pets and livestock. Kane is based in Seattle.
1. Kirkham WW, Guttridge H, Bowden J, et al. Hematopoietic response to hematinics in horses. J Am Vet Med Assoc 1971;159(11):1316-1318.
2. McKeever KH, Agans JM, Geiser S, et al. Low dose exogenous erythropoietin elicits an ergogenic effect in standardbred horses.
Equine Vet J Suppl 2006;36:233-238.
3. McKeever KH, Agans JM, Geiser S, et al. Effect of recombinant human erythropoietin administration on red cell volume, aerobic
capacity and indices of performance in standardbred horses, in Proceedings. 16th Equine Nutr Physiol Symp 1999;163-164.