Mythbuster Monday: Running A Horse on Lasix Is ‘Safe’ Even If It’s Not a Known Bleeder
On Mythbuster Monday, we tackle a variety of equestrian myths to either bust or confirm. Today’s discussion: Is it safer to run a horse on Lasix even if the horse is not a bleeder?
It’s Mythbuster Monday, where Horse Nation dives into different equestrian myths and provides research-based evidence to either bust or confirm those myths. Today’s topic: Is it safer to run a horse on Lasix even if the horse is not a known bleeder? What does Lasix do? What are the best options before starting a horse on Lasix? Read further to find out!
Myth: It’s safer to run a horse on Lasix even if the horse is not a known bleeder
Myth or Fact: Myth
Lasix, generic name furosemide, is a diuretic that decreases sodium absorption in the kidneys, causing the horse to urinate more often. Horses treated with Lasix lose 40 – 50 times more sodium and chloride within the first four hours following administration than a horse that is not on the medication.
Water makes up 65 – 75% of a horse’s blood volume. When on Lasix, the horse excretes more water through urine, thereby reducing blood volume, blood pressure, and the horse’s overall weight. According to an article by Mad Barn, a horse treated with 150mg of Lasix could lose up to 28 pounds in four hours!
Other side effects of the drug include extreme dehydration, electrolyte issues, increased risk of colic, and heart arrhythmias. While some will offer access to water and provide electrolytes that way, horses on Lasix were not found to increase water intake until 20 hours after administration of the drug. Horses on Lasix do not return to normal hydration levels for at least 24 hours after administration.
So, is it safe to run a horse on Lasix even if the horse is not a bleeder?
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Exercise-Induced Pulmonary Hemorrhage (EIPH) is a hemorrhage of the pulmonary capillaries in the horse’s lungs, resulting in nose bleeds. The condition occurs during strenuous exercise. Most performance horses will experience some degree of EIPH, however the majority will not suffer any effects from it. Those affected from EIPH are the horses at grade 4 on the EIPH scale. Grade 4 is when the horse exhibits multiple streams of blood that cover over 90% of the trachea. The degrees of EIPH are as follows:
So why do people use Lasix if their horses are not known bleeders? It has been shown that horses on Lasix run faster and earn more money over their careers than those not on the drug. Therefore, many are now using the term without proper diagnosing to administer the drug as a performance enhancing agent. However, Lasix does have its consequences. Mad Barn also reviewed Thoroughbred racehorses found that Thoroughbreds medicated with Lasix on race day had 62% greater odds of sudden death due to fatal arrhythmia.
This article suggests the horse owner consult with the veterinarian to determine the appropriate use of Lasix. An EIPH diagnosis should be given to the horse in way of endoscopy or broncho-alveolar lavage before considering the use of Lasix. They also suggest properly conditioning the performance horse. It is essential for horses to be in optimal shape before running full out to aid in respiratory and cardiovascular health. Safer options included in the article are nasal strips, concentrated equine serum, and Omega-3 Fatty Acids.
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Vetline Equine published a study completed by race trainer, Kiaran McLaughlin. For two years, McLaughlin kept all of his horses off Lasix and scoped them directly after each race. Results showed that less than 5% of horses showed any bleeding. After completing this study, he urges phasing out the use of Lasix on horses and trying alternative treatments.
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Another study, published by Daniel Ross, showed that out of 415 horses with a diagnosis of EIPH, 273 of the horses bled at a level one or not at all. These horses performed just as well as the horses in the study that did not have a diagnosis of EIPH. Only 13 horses in the study were diagnosed with a level 4 severity of EIPH.
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In April 2024, Washington State University was granted more than $370,000 to complete a two-year study on the impact of Lasix administered to racehorses prior to their race. The study is being completed because many are now questioning the performance aspect of the drug and its influence on other health issues. Based on the findings of this particular study, the Horseracing Integrity and Safety Authority will determine if Lasix will be a prohibited drug by 2026. They expect other disciplines to follow suit.
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After diving into the research, Lasix is a drug that should be used for horses with a known diagnosis of EIPH. Side effects if used for performance enhancing include electrolyte imbalances, arrhythmias, and sometimes sudden death. It’s important to consult your veterinarian, obtain a scope, and get a proper diagnosis before starting your horse on any medication.
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