Dr. Cody Johnson’s experience has informed his belief that a restricted airway and inflammatory airway disease are the vast majority of causes for bleeding in barrel horses. Photo by Tammy Sronce

Administering Lasix to barrel horses has gotten mixed reviews. Are concerns valid?

Furosemide—trade name Lasix—is a valuable medication for the treatment of exercise-induced pulmonary hemorrhage (EIPH) in racehorses. It’s also become an important tool for many barrel racers, since the high exertion inherent to competition can instigate the lung bleeding associated with EIPH. But the drug has raised concerns for some horsemen, and in recent years it was even briefly on the American Quarter Horse Association’s banned substance list for competition. Let’s look at how furosemide affects the horse and why it’s controversial.

EIPH Explained

Cody Johnson, DVM, is an equine sports medicine specialist at Elgin Veterinary Hospital in Elgin, Texas, with a vast amount of experience evaluating hard-running performance horses as well as treating and diagnosing “bleeders.” Exercise-induced pulmonary hemorrhages occur when a horse’s body is performing at maximum exertion and the body is struggling to compensate.

“At that point, there’s a decrease in airway pressure and an increase in blood pressure,” Johnson said. “Their body is pumping more and more blood trying to oxygenate, and you’ll see bleeding at the capillary level.”

Racehorses and barrel horses experience EIPH issues in different ways, Johnson says. Racehorses—particularly Thoroughbreds—run longer distances and experience maximum exertion at a later part of the race. Johnson says that is the point where the horse may bleed.

racehorses running
Racehorses and barrel horses experience exercise induced pulmonary hemorrhage issues in different ways, since maximum exertion occurs during different parts of their respective races. Photo by Danika Kent

“At maximum exertion, their blood pressure is going to rise as their body is trying to produce enough oxygen to supply the muscles,” Johnson said. “That is where you see the bleeding occur.”

A barrel horse is a short-distance sprinter, blasting top speed between the barrels. Maximal exertion is reached between the barrels as horses accelerate and decelerate in short bursts, which can require them to hold their breath at times and take deeper breaths at others. To turn a barrel at top speed, a horse must time its breathing correctly, which usually results in a deep breath taken between barrels. This point of the run is where veterinarians believe bleeding occurs.

Johnson says there are three main causes of pulmonary bleeding in horses. One is idiopathic, meaning the lungs are healthy but the pressure difference of the vasculature and the airway causes them to bleed.

horse leaving a barrel
Johnson says many barrel horses take a deep breath when sprinting between barrels, which is when it is believed bleeding is most likely to occur. Photo by James Phifer

“These horses are not predisposed to [bleeding] for any reason, it’s simply the difference in pressures at maximal exertion which results in rupturing of the capillaries within the airway,” Johnson said.

Another cause is a restriction in the airway. Johnson says restrictive airways can be from multiple disease processes, including laryngeal hemiplasia (bad flapper), dorsal displacement of the soft palate, cicatrix, arytenoid chondritis, and many more. These are diagnosed by endoscopic examination of the airway.

“In these cases, the horse is likely to bleed because they cannot pull as much air in due to the airways being restricted,” Johnson said. “This results in a larger decrease in the amount of pressure within the lungs as blood pressure rises, causing bleeding.”

A third cause is an inflammatory airway or obstructive airway disease deep in the lungs, such as asthma or chronic obstructive pulmonary disease (COPD).

“With excessive inflammation, the alveola cannot stretch the way it needs to, so you get both a difference in the pressure gradient and you get the irritation effect of the inflamed area,” Johnson said. “That results in bleeding.”

Johnson says in his experience, a restricted airway and inflammatory airway disease are the vast majority of causes for bleeding in barrel horses. In a study published in a 2016 Journal of Veterinary Internal Medicine, 170 Canadian barrel horses were tested at random for EIPH post-race by scoping the trachea looking for blood. The study showed 45 percent of the horses bled post-competition.

“My personal opinion is the vast majority of horses competing in barrel racing bleed at some point in their career,” Johnson said. “I think it’s a prevalent problem, and it affects more horses than we think.”

Scoping the trachea doesn’t always catch minor bleeds, Johnson says. An average barrel race may not create a substantial bleed that can be visible on a scope. But a bronchial alveolar lavage (BAL) is another way to diagnose bleeds.

“You insert a tube, fill a small portion of the lung with saline and pull the saline back out. The sample you collect contains inflammatory cells present within the lungs as well as any blood cells. Cytology of the sample allows us to determine if inflammatory airway disease is present and gives us information about how to treat it,” Johnson said. “I think it’s a better diagnostic tool for whether or not a horse is bleeding. It’s a little more invasive, so it’s not something you would do at a barrel race. But it has shown us the prevalence of this disease process is probably higher than what has ever been recorded.”

How Lasix Helps

Furosemide acts on the kidneys. It’s a diuretic, which increases the amount of salt the kidneys excrete, which also excretes more water, Johnson explains. The drug also works on the horse’s vasculature, lowering the pressure on the pulmonary arteries and veins by increasing their elasticity, which Johnson says helps reduce instances of EIPH.

“Studies have shown Lasix does decrease the pressures within the blood vessels inside the lungs, which lessens the severity of EIPH,” Johnson said. “You’re giving the lungs a little help, so that in the event they have these conditions, you’re helping to protect from the bleeding occurring. That’s the major reason why Lasix is allowed on race day and should be allowed on race day, because it is a preventative of the negative effects of EIPH. By using Lasix as a preventative, we are protecting the welfare of the horse and hopefully allowing it to have a longer and healthier career.”

person giving a horse an IV shot
Lasix has raised concern for some horsemen but is the only preventative of exercise induced pulmonary hemorrhage that scientifically has been shown to work, according to Cody Johnson, DVM. Shutterstock photo

Most veterinarians and equine professionals agree there is no drug or remedy as effective at preventing bleeding as Lasix.

“Lasix is the only preventative of EIPH that scientifically has been shown to work,” Johnson said. “Now, in research, some papers say it works, some say they didn’t see a reduction in the prevalence of EIPH, but they did see a change in the severity of the disease. Anecdotally, I think all racetrack practitioners would agree it works, and it is very reliable.”

Side Effects

As with any drug, Lasix has some negative side effects. The greatest is dehydration, Johnson says.

“It’s a diuretic, so you are dehydrating the horse,” Johnson said. “Because it works at the kidneys, there can be some electrolyte imbalances seen. It is a potassium-wasting drug—it lowers the amount of potassium in the serum, which can have effects on the heart and muscles. These side effects are extremely rare when we supplement with electrolyte pastes before the run. The benefits of Lasix far outweigh any risks.”

When Lasix is administered, the horse’s intake of water is restricted. For a horse traveling on the road, it can be difficult for the horse to regain hydration unless there is careful management.

“Most horses do fine, but if you give it to a horse that is already dehydrated, the negative effect of the drug is going to be worse,” Johnson said. “It’s best to give it to horses that are well hydrated and drinking well.”

Why It’s Controversial

Lasix has a negative connotation to some horsemen, who see administering the drug as an admission that their horse is a “bad bleeder.” Johnson disagrees, saying early use can help reduce the severity of potential bleeds and protect the horse from the serious long-term effects of EIPH.

“It would be better to have more horses on Lasix actually, to prevent bleeding before it occurs, so we don’t get bad bleeders in the long run,” Johnson said.

Others in the horse industry argue the drug acts as a performance enhancer.

“You can see it as a performance enhancer in two ways,” Johnson said. “One is yes, they are less likely to bleed, so yes, it does help a horse with the potential to bleed. But it’s something the horse needs, and it also protects the horse from future problems.”

Some argue the weight loss associated with diuretics enhances performance.

About Cody Johnson, DVM

“The other side is the weight loss, because of the diuretic effect and whether or not that’s a performance enhancer,” Johnson said. “I think it can go either way. Some horses may run a little better on it, some horses run a little worse. I think they respond to it on an individual scale. But I don’t believe it truly falls under a performance-enhancing drug category.”

Johnson stresses that Lasix should really be looked at as a preventative measure for EIPH—not treatment for bad bleeding. Once a horse has EIPH, Lasix doesn’t always stop the problem.

“By the time you have a horse that is a ‘bad bleeder,’ Lasix will do very little to help,” Johnson said. “The bleeding changes the physiology of the lungs. When they bleed, the lung has to heal. All those capillaries have to heal. So then you get some thickening of the blood vessels in the lung, and you also get scar tissue within the lung. At that point, Lasix is not necessarily going to work every time.”

Beginning to administer Lasix earlier in the horse’s career before EIPH develops will help reduce the chances of the disease progressing into a problem, Johnson says. He wants to change the stigma that a horse running on Lasix is already a chronic bleeder.

“Putting a horse on Lasix means you are trying to prevent him from having EIPH, so you can increase his performance lifespan,” Johnson said.

In the racing industry outside the United States, the use of medication of any kind on race day is strictly prohibited. In America, Lasix is the only acceptable medication for race day, though it is frowned upon by some. Johnson says research is being conducted to discover how far before a competition the drug can be administered to still help the horse and reduce race-day medications.

“We have to remember we are here for the welfare of the horse,” Johnson said. “We have to do what is right for the horse. We [as veterinarians] look at Lasix from a welfare basis—this is a preventative measure to reduce EIPH, bleeding into the lungs. That is not a benign occurrence, and when that happens it sets the horse up for a lot of problems—pneumonia being one of the major ones.”

When To Use Lasix?

girl taking off horse's boots after a run
Johnson says in his experience, a horse that takes longer than one minute to recover after a run should be evaluated. Photo by Kailey Sullins

How can you tell if your horse is a candidate for Lasix? Don’t assume your horse needs to be a bleeder before looking into Lasix. Johnson says some indications your horse could be suffering from early signs of EIPH include coughing after a run and slower recovery post-run—longer than 60 seconds for your horse’s respiration to return to resting is abnormal.

“If a horse is making really good runs but just isn’t clocking anymore, that’s a sign,” Johnson said. “A horse taking longer than a minute to recover should also be looked at.”

Johnson recommends having your veterinarian scope your horse’s trachea if you have any concern bleeding is occurring. If nothing comes up, you may want to invest in a BAL for further diagnostics.

Once you find out if your horse is bleeding, you need to be vigilant about doing everything you can to prevent bleeding from occurring or becoming worse. This can include a more rigorous conditioning routine to ensure the lungs are in top shape and taking efforts to reduce allergens, such as dust, in your horse’s environment. Simply feeding hay on the ground instead of an overhead bin or not tying your horse’s head in the trailer can reduce the allergens that reach the lungs.

Johnson says more research on EIPH is needed to possibly find other methods of treatment and prevention. For now, he believes Lasix is the best course of preventative treatment.

“There’s a lot of anecdotal information out there, rumors and myths associated with EIPH,” Johnson said. “I think it’s very important for owners to utilize their veterinarians’ knowledge and ability to research and share information. It’s easy to want a quick fix for the problem. Work with your veterinarian, who is knowledgeable about medication and the disease process, to learn about EIPH.”

This article was originally published in the January 2018 issue of Barrel Horse News.

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