The Fatalities at Santa Anita — is it the Lasix?

One of the potential culprits identified for the cause of the breakdowns at Santa Anita are the drugs that proliferate among horse trainers. Not illegal drugs, but “medications” that prevent horses from bleeding or drugs that mask pain to the point where the horse is at more danger of injuring itself. After all, some pain is good because it prevents horses from running.

Recent changes at Santa Anita put the track more in line with international standards. The California Horse Racing Board approved proposals by track owner, the Stronach Group, which owns Santa Anita, to ban medications given to horses on the day they race. The most controversial decison? To ban Lasix.

Why are horses given Lasix?

Lasix, or furosemide, is given to horses to prevent exercise-induced pulmonary hemorrhaging (EIPH), a problem which is systemic in horses. Before understanding why racehorses are given Lasix, you first need to understand why horses experience bleeding in their lungs.

A horse’s spleen stores extra red blood cells and dumps them into circulation during exercise. The increase in red blood cell volume boosts oxygen delivery and aerobic performance but only up to a certain threshold, which is different for each horse. Once this optimum threshold is breached, cardiac

Horse bleeding from EPIH
An example of epistaxis, grade 4 EPIH. Only 1-2% of horses experience this level of bleeding.

output and aerobic performance begin to decline due to the increase of blood viscosity [1].

Current evidence suggests that increased blood viscosity of exercising horses contributes to blood flow resistance and high blood pressure in the lungs, causing capillaries in the lungs to rupture [3]. Hemorrhaging blood accumulates in the interstitial spaces and alveoli, which can be detected using endoscopy. A spike in blood viscosity that goes beyond a horse’s optimum threshold level during intense exercise is the key factor that increases capillary wall stress and causes capillary vessels to burst.  From Why do Horses Bleed?

Now, the above sounds pretty serious, except that not all horses experience serious bleeding. There are technically five classes of (EPIH).  More than fifty percent of thoroughbreds do not bleed at all (class 0); the majority of those horses who do bleed are are classified as grade 1-2, which is bleeding so minor that can only be detected through an endoscope; grade 3 is more serious; and grade 4 is epistaxis, which is bleeding through the nostrils.

A 2005 study of 744 racehorses in Australia – where Lasix is banned on race-day but permitted for training purposes – found that horses that bled to a degree less than one were four times more likely to win than horses that bled to a level higher than two. Lasix: the drug debate which is bleeding US horse racing dry

The Australian study also showed a direct correlation between the nuber of times a horse is scoped and wehter or not they show signs of bleeding:  Between 43% and 75% of racehorses exhibit signs of EIPH based on the evidence of one scope. The 2005 Australian study showed that nearly 100% of horses scoped after three successive strenuous workouts showed some bleeding by the third endoscopic exam.

So why then, you might ask, do most horses in the US get race day Lasix, regardless of whether or not they bleed? Because it makes them faster.

How Lasix works
Diagram from

Lasix is a strong diuretic that increases urine production and urinary frequency. Since Lasix reduces plasma volume by 11-13%, many experts believe it reduces blood pressure in the lungs and prevents bleeds from occurring. The protocol is to give the drug four hours before a race and to withhold feed and water. Whether or not Lasix actually prevents bleeding is controversial. What is incontroversial is that Lasix causes immediate and significant weight loss, which makes it a performance enhancing drug.

Researchers found that when feed, hay and water were withheld for 4 hours, untreated horses lost an average of 9 pounds. Horses treated with 150mg (3cc) furosemide lost 28 pounds, those treated with 250mg (5cc) lost 31.5 pounds and those treated with 500mg (10cc) lost 32 pounds. Use of Lasix in Horses

This weight loss is significant because a lighter horse expends less energy and takes longer to fatigue. In other words, Lasix makes horses more competitive. The effect of race-day dosing of Lasix was explored in a peer-reviewed study published in the Sept. 1, 1999, issue of the Journal of the American Veterinary Medical Association. Its title: Effects of furosemide on performance of Thoroughbreds racing in the United States and Canada.

The authors analyzed 22,589 race records provided by the Daily Racing Form. These records were of horses that finished a race on a dirt surface in the United States and Canada between June 28 and July 13, 1997, in jurisdictions that allowed the use of furosemide. Of that total, 16,761 (74.2%) had been administered Lasix. The authors concluded that:

“Horses that received furosemide raced faster, earned more money, and were more likely to win or finish in the top 3 positions than horses that did not. The magnitude of the effect of furosemide on estimated 6-furlong race times varied with sex with the greatest effect in males.”

When comparing horses of the same sex in six-furlong races, the authors determined the difference between racing with Lasix versus without was 3 to 5.5 lengths.  The Performance-Enhancing Effects of Lasix

Animal Kingdom wins Dubai World Cup
Animal Kingdom raced on Lasix when he wone the Kentucky Derby. There were questions about how he would perform lasix-free in the Dubai World Cup. But he laid down a great run.

Now, it needs to be noted that the US is the only country where race-day Lasix is allowed, so there are thousands of horses racing successfully in other countries. And, until 30 years ago, Lasix wasn’t used in the US either. In fact, widespread use of Lasix may be bad for future generations of thoroughbreds because it does not weed out horses that are bleeders from the gene pool.

Some of the country’s other biggest tracks have joined Santa Anita and Golden Gate Fields in phasing out Lasix, including Churchill Downs, Pimlico and Belmont, hosts of the Triple Crown series. The newly formed coalition includes Saratoga in upstate New York and Del Mar near San Diego, which stage the summer’s highest-profile races. They all agreed to phase out the use of the drug starting next year.

In 2021, the ban would extend to all horses competing in any stakes races at tracks in the coalition. That’s when the Triple Crown would be run for the first time under the new medication rules.

One thought on “The Fatalities at Santa Anita — is it the Lasix?

  1. I am not sure that the use of Lasix is safe for horses. Not to mention, unsportsmanlike. It’s good that someone paid attention to this. Horses suffer from EIPH, and they suppress it in such a terrible way. What a shame!

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