Lung bleeding, technically known as EIPH — exercise induced pulmonary hemorrhage — is a potential problem for any horse that performs at high speeds.
Studies have repeatedly shown that at least low-level evidence of pulmonary bleeding can be found in over 95% of horses performing at speed. Some bleeders actually do show blood draining from the nostrils, but many horses are believed to bleed in the lungs and go virtually undetected until they’re scoped and diagnosed by a veterinarian.
Bleeding certainly does influence performance. At what point that begins to happen is difficult to quantify, especially since one commonly cited study found a high percentage of bleeders among racehorses that had won their races.
However, two other studies reported only about half as many bleeder horses as nonbleeders do well racing. Common sense alone would tell you that areas of the lungs that are filled with blood aren’t functioning in taking up oxygen and getting rid of carbon dioxide.
There are long-term consequences as well. The presence of blood in the lung causes a significant inflammatory reaction that leads to thickening of the lung tissues, again making them less efficient or totally nonfunctional in terms of gas exchange. In addition, the horse with free blood in his lungs is at high risk of developing a variety of infections.
In a nutshell, anything that leads to abnormally high pressures along the capillaries of the lung can cause bleeding. A significant factor in lung bleeding is the high pressure that develops in the vessels of the horse’s lung during exercise, especially the tiny capillaries, where walls are thinnest and where gas exchange occurs.
Furosemide (Lasix or Salix) is the only drug that reliably reduces the amount of lung bleeding, although it doesn’t completely prevent it. This is because furosemide lowers the high vascular pressures. However, studies have also shown that there is no significant difference between intravascular pressures during exercise in horses that bleed versus horses that don’t, so there must be other causes operating here.
Many experts think the real answers as to why horses bleed have to do with factors that involve the lung tissue itself and pressures in the airways. In fact, a Kansas State study concluded that changes in the pulmonary artery pressure could only account for 20% of the variability in levels of EIPH seen in racing horses.
The documented ability of Flair Nasal Strips to at least reduce symptoms of lung bleeding is an example. By lowering resistance to air flow, bleeding was reduced. Anything that interferes with the ability of the horse to breath easily, from anatomical problems to allergies, can increase the risk of bleeding.
Obviously, no single drug, device or supplement can eliminate the risk of lung bleeding. How well anything works depends on the risk factors operating in the individual horse, so we can’t give you a blanket recommendation, beyond furosemide, which is a prescription drug. Nasal strips do at least reduce air resistance, but they may not be legal under your competition’s rules. Be sure you check.
Your best bets on the supplement front are products that work to improve the strength/integrity of capillaries, minimize or help eliminate mucus and control allergic/irritative reactions in the airways and the lungs. We’ve listed good choices in our accompanying chart. Pay attention to the indications to make the best selection for your horse. Please note these products primarily address any possible lung problems contributing to elevated pressures across capillary beds.
Don’t waste your money on products that don’t disclose their ingredients or supposedly are “natural” alternatives to diuretics/furosemide. Some herbal/natural diuretics are potentially toxic. Vitamin K, a nutrient essential for normal clotting, is a common ingredient in supplements for bleeding, but we can find no evidence to suggest vitamin K deficiency is ever involved.