Facts, opinions, and conclusions for the handicapper.

In this article, we will examine a number of questions. You may read through the document top-to-bottom or jump directly to the topic that interests you.


In the 1960s, the use of Lasix to prevent bleeding was virtually unknown. Today, every racing state permits the use of raceday Lasix treatments, and in many locales, the number of horses racing on Lasix is greater than the number racing without.

This rapid increase in Lasix use has been attributed to a number of factors. Indiscriminate breeding in the 1970s to meet the increasing demand for racing stock is blamed for weakening the breed. Pollution in the air and water irritates horses' systems. And year-round racing takes its toll on thoroughbreds by offering fewer breaks and more varied racing climates.

Although most handicappers understand the general implications and effects of Lasix use, most do not comprehend why it is necessary or how it works. And many inexperienced fans do not even know what it is. This article explores all these topics, and suggests how handicappers can benefit from this knowledge.

A lesson in equine physiology: the biological reasons for bleeding

The thoroughbred racehorse has been highly optimized over hundreds of years of breeding to be an extremely efficient runner. Why, then, do so many of the species suffer from bleeding in the lungs under the stress of running? The answer to this question requires a peek inside the horse; understanding the configuration of the horse's internal organs shows why some bleeding is inevitable during a race.

The technical name for "bleeding" is exercise-induced pulmonary hemorrhage (EIPH). This describes a condition in which the tiny blood vessels in a horse's lungs rupture due to stress sustained during physical exertion. EIPH occurs in three variations. Simple EIPH is an acute condition resulting from the strain of exercise. Patent pulmonary hemorrhage (PPH) involves bleeding in the lungs as a reaction to an allergen, infection, or due to hypertension. Some horses experience composite bleeding, which is the result of the combined effects of simple EIPH and PPH. PPH is a chronic condition which must be treated with various medications. The effects of simple EIPH heal naturally over the course of several days.

Simple EIPH occurs as the natural consequence of strenuous running due to the layout of the horse's organs and the way the equine body moves during high-speed galloping. The horse's body is divided into two halves. The front end of the horse's trunk contains the heart, lungs, and other major organs. The back half of the horse contains the intestines, which are suspended within the abdomen by ligaments. The two halves are divided by a thin sheet of muscle called the diaphragm.

When the diaphragm contracts, the effect is to increase the volume of the horse's front half, the chest cavity. This increased volume draws air into the lungs. When running, this movement is synchronized such that the horse inhales when his front feet hit the ground and his skeletal structure is stretched to its maximum length. When the horse's front feet leave the ground, the skeletal structure is compressed and the diaphragm relaxes. The constricting chest cavity forces air out of the lungs, and the horse exhales.

Due to the back-and-forth motion of galloping, the horse's intestines swing like a pendulum at the end of the suspensory ligaments. When running at full speed, especially in the fastest sprint races, the movement of the intestines can get out of phase with the movement of the diaphragm in such a way that the intestinal mass is swinging forward as the horse is trying to exhale. This causes the diaphragm to be slammed forward and slightly upward. The diaphragm, in turn, squeezes part of the lungs against the chest wall.

The lungs are filled with alveoli, tiny air sacs, and capillaries, miniscule blood vessels. The alveoli and capillaries are so fine and so interconnected that oxygen from the inhaled air can pass into the bloodstream, and carbon dioxide in the blood can pass out of the blood into the lungs to be exhaled. The capillaries are at their smallest and most efficient near the rear, tapered end of the lungs where they abut the diaphragm.

It is exactly these most efficient, extremely fine capillaries which are repeatedly impacted by the forward-surging intestinal mass. As they rupture under the stress, the horse's air passages become clogged with blood. Obviously, this causes difficulty in breathing which causes difficulty in running.

Some studies suggest that airborn debris, such as dust and pollen, play a role in EIPH. Increased fluid and mucous or inflammation due to these irritants obstruct the horse's airways and require even harder breathing during a race.

Once EIPH starts in a horse, it tends to be a lifelong problem.

The role of Lasix

The medication Furosemide, sold under the trade name, "Lasix", is a powerful diuretic that causes fluids locked up in the horse's body tissues to be released and expelled in the urine. This has the effect of lowering the horse's blood pressure, particularly in the aorta and pulmonary artery. The lower blood pressure in the capillaries mitigates the problem of EIPH; thus, the horse's performance returns to a normal level. Lasix is treatment of choice for EIPH, though study results of its effectiveness vary.

Some experts contend that Lasix has a stimulating effect on some horses that enhances their performance beyond what it would normally be. Furthermore, some suggest that the sheer volume of fluid lost by the horse (up to several gallons) can cause it to lose as much as twenty pounds, giving it a weight advantage. (Considering the fact that the imposts carried by different horses in a handicap race my vary as little as five to ten pounds, a twenty pound reduction in weight may be very significant.)

Furthermore, there are those who suggest that the increased urinary output of the horse flushes away traces of other, illicit, performance-enhancing substances in the bloodstream.

The scope of the problem

Virtually every equine athlete that is required to gallop for prolonged periods is susceptible to the effects of simple EIPH -- bleeding caused by the strain of exercise. However, the problem is most widespread in thoroughbreds because they maintain a high speed for up to two minutes or more. The problem is less severe in steeplechasers, standardbreds, and heavy draft horses because they run at slower speeds due to the nature of their competition.

It is estimated that two to three percent of thoroughbreds bleed so severly as to be evident without the aid of medical equipment. However, a large majority of horses race on Lasix in jurisdictions where it is legal.

If a horse bleeds during a race, and the blood is detected during a veternary examination after the race, it is declared a "bleeder" and permitted to race with the medication, Lasix.

Though only a small number of horses overtly bleed due to EIPH, nearly all horses show at least some bleeding deep within the lungs. This can be detected by a bronchoscope. Thus, if a trainer wishes to put his horse on Lasix, he can simply have the horse "scoped" after the race. The examination will almost certainly turn up traces of blood in the lungs, and the horse will be able to race with the benefit of Lasix in future races. Thus, practically any horse can be treated with Lasix if its connections so desire.

The role of Butazolidin

Phenylbutazone (PBZ), sold as "Butazolidin" and commonly called "Bute", is a non-steroidal anti-inflammatory drug (NSAID). In most states, it is the only medication, besides Lasix, permitted in a horse's bloodstream during a race.

Like the common human NSAID, aspirin, Butazolidin fights pain, inflammation, and fever. It is normally used as a theraputic drug to treat sick or injured horses. One side effect of NSAIDs is to decrease the platelets in the bloodstream which causes "thinner" blood. Some suggest that the problem of EIPH is exacerbated by thinned blood. Another negative side effect is that prolonged use of Butazolidin can cause ulcers and gastrointestinal irritation in horses.

"Bute" does not enhance performance in any way; however, a trainer with his bottom line rather than the horse's welfare in mind could use Butazolidin to numb a horse to the pain of an injury so that it can continue to race when it should be laid off.

The Lasix debate

Opponents of Lasix use point out that it was legalized in the late 1970's during a shortage of thoroughbreds in North America. They suggest that Lasix and Butazolidin are used to make otherwise uncompetitive horses able (if not fit) to race.

They are also quick to note that the percentage of winning favorites has declined since the introduction of these drugs -- a sign that racing has become less formful. Furthermore, they assert that the commonplace use of a controlled substance in racehorses does not contribute to the image of racing as a fair and legitimate sport.

Lasix proponents simply assert that it is a treatment without which certain horses would be unable to race due to physical ailments. Many horses are bleeders and require medication to control the problem.

Many people from both sides agree, however, that the use of Lasix and Butazolidin is getting out of control. Since virtually all horses bleed -- at least a little bit -- any horse can be declared a bleeder and put on Lasix. Bute can be used on any horse the trainer deems needs it. Why the proliferation of horses racing with Lasix and Bute?

Some say that trainers are using both drugs just in case their horse has an undetected problem. Or, they may be using them because there is a perceived advantage to using these drugs, and they do not want their horses to be at a disadvantage.

At the very least it can not be denied that the large majority of horses race under medication on a consistent basis. One finds oneself wondering if these drugs are truly necessary on a continuing basis. And if so, should such horses be permitted to race?

The practical implications

Regardless of which side one takes in the Lasix debate, it appears that controlled medications are here to stay. Lasix and Butazolidin are legal and common in most jurisdictions, and more theraputic drugs may be permitted in the near future. For instance, California is considering establishing maximum bloodstream levels of eight drugs. The issue of horses running on medication seems to be expanding.

Since medications will be a part of racing for the foreseeable future, it is prudent for the handicapper to carefully consider the impact of these chemicals whether you call them "theraputic medications" or "performance-enhancing drugs". The use of raceday medications entails a number of implications of practical value to the handicapper.

Consider first the mechanism by which bleeding occurs; the horse's intestines move out of sync with his breathing, causing his lungs to be battered by the intestinal mass. This may explain why the practice of "drawing" a horse, or witholding feed for six to twelve hours prior to a race, is an effective trick to maximize performance. While there is no way for the handicapper to tell whether a horse had been drawn, the astute observer can certainly watch to see if any horse makes a move to lighten his intestinal load in the paddock or post parade immediately prior to a race.

Also consider the type of exercise that leads to hemorrhage -- very fast galloping. This implies that sprinters, who run the fastest, have the most to gain from using Lasix. Routers enjoy a slower pace and probably incur less damage to their lungs during the typical race.

Certainly one should study a horse's past performances very carefully before playing the "first time Lasix" angle. Is this a horse that can benefit from a dose of Lasix? Typically, a horse that shows early speed then suddenly stops after a half mile or so is likely to be suffering from the effects of bleeding. This is the type of horse that can be helped by Lasix. Horses that run near the back of the pack throughout the entire race are unlikely to improve under any medication.

Some professional handicappers suggest that Lasix is least effective on hot, humid days, probably because any mammal's breathing is more difficult on such days.

If your handicapping typically involves favoring horses carrying less weight than their rivals, be sure to take into account the pounds shed by a Lasix-medicated horse by increased urinary output.

It seems evident that the effects of EIPH are efficiently healed because most horses perform well after only 10 to 14 days between races. However, it is natural to suppose that years of racing might leave a fair amount of scar tissue on a horse's lungs. Therefore, it might be worthwhile to consider how well older horses will be able to breathe during a particularly strenuous race.

Keeping the causes of EIPH and the effects of Lasix in mind when handicapping should provide some insights into how medicated horses will perform in a given race. However, these handicapping suggestions should be kept in perspective. Incorporate them into your overall method of handicapping, but do not place undue emphasis on them.


  1. Ainslie, Tom, Ainslie's Encyclopedia of Thoroughbred Handicapping.
  2. Biles, Deidre B., "The EIPH Puzzle". The Blood Horse, 04JAN97.
  3. Grening, David, "How Lasix Came To Be in New York". Thoroughbred Times, 26AUG95.
  4. Kopp, Kenneth J., D.V.M., "The Danger in Dust". The Mane Points, Spring 1996.
  5. McArdle, Camille J., "At the Threshold". Thoroughbred Times, 06MAY95.
  6. McArdle, Camille J., "Bute: Then and Now". Thoroughbred Times, 17JUN95.
  7. O'Dea, Joseph C., "A Trail of Blood". Thoroughbred Times, 11MAR95.
  8. O'Dea, Joseph C., "Racing and the New York Rule". Thoroughbred Times, 18MAR95.
  9. Williams, George, "Perspectives on the Use of Lasix". Thoroughbred Times, 26AUG95.


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