Bits can suffocate racehorses and cause sudden death, suggests professor


bit-sideSudden death results from a man-made problem stemming from the mouth that spawns increasingly serious problems in the throat, lungs and heart. A bit breaks the lip seal during strenuous exercise, destroys what should be a vacuum in the mouth, releases the soft palate from its locked-down position, and allows the throat airway to collapse. Death follows from suffocation, waterlogging of the lungs and heart failure.

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An emeritus professor of veterinary surgery describes this sequence in a paper published online ahead of print in the peer-reviewed journal, Equine Veterinary Education.

Dr Bob Cook, from the Cummings School of Veterinary Medicine at Tufts University in the United States, notes that there is no consensus on the cause of sudden death in racehorses, despite several racing jurisdictions having mandated necropsies for years.

Cook’s research since 1958 into ear, nose and throat diseases of the horse led him, in 1997, to investigate the effect of a bit on a horse. He went on to develop a widely used bitless bridle.  He reasons that “bleeding”, as it is known in racehorses, is the same as an airway emergency in human medicine known as negative pressure pulmonary oedema.

Cook – a pioneer in the use of the rigid endoscope – was the first to conclude, in 1970, that when a racehorse showed blood at both nostrils this came from the lungs, not the nose or throat as previously assumed.

When flexible fiberscopes became available, Richard Pascoe in Australia confirmed this and used the term exercise-induced pulmonary haemorrhage (EIPH) to describe it.

In 1998, Cook’s team at Tufts first suggested that the mechanism for EIPH was asphyxia.  EIPH in racehorses led to a controversial policy – justified as prevention – that permitted US racehorses to be given the diuretic furosemide on race days.  Furosemide did not prevent EIPH, yet the majority of American racehorses still run on this medication.

Cook now proposes that, although a neurological disease of the voice box can occasionally trigger asphyxia, lung bleeding and even death, the evidence is more consistent with the bit being the cause. He believes that prevention of both EIPH and sudden death requires an equipment rule change around bit use rather than medication or surgery.

Cook compared his ante mortem data on sudden death with a 2011 review of post mortem data from mandated necropsies in six racing jurisdictions worldwide.  He concluded that the data comparison supports a unifying hypothesis on the cause of three unexplained problems – that the bit is the ultimate cause of soft palate instability, “bleeding” and sudden death.

A racehorse in Germany. Dr Cook notes the sealed lips, the lack of drooling and the loose rein.
A racehorse in Germany. Dr Cook notes the sealed lips, the lack of drooling and the loose rein.

He recommends bitless training and racing trials to show stewards that bitless racing is both possible and preferable and will reduce the prevalence of all three problems.

Cook writes: “The speed with which death occurs suggests its cause, there being few things that can kill a horse in a matter of seconds … A horse can survive for weeks without food, days without water but only seconds without air.

“Aside from asphyxia, only cardiac failure kills as quickly. As cardiac disease in the racehorse is rare and as cardiac failure can be a sequel to asphyxia, asphyxia is clearly a candidate for the cause of sudden death.”

Cook says that in the wild a horse runs with its lips closed, mouth shut, tongue immobile, poll extended, the head/neck pendulum unhindered, balance perfect, with no slobbering.

“But because of bit usage, many racehorses run with their poll flexed, mouth agape, lips parted, tongue protruding, head/neck pendulum constrained, balance upset and saliva streaming.”

Such horses are, he says, denied the oral vacuum that keeps the soft palate in its locked-down position, and also denied the ability to breathe, balance and conserve energy. Horses are nose breathers, not mouth breathers.  Surgery, in his opinion, is not the answer to instability and dorsal displacement of the soft palate.

According to Cook, bit-induced obstruction of the throat airway accounts for abnormally intense and accumulating suction pressures in all ensuing sections of the airway when a horse breathes in. As a galloping horse takes two and a half forceful breaths a second, even transient airway obstruction can quickly cause serious consequences.

It accounts for the endoscopically observed dynamic collapse of the soft palate and many other areas in the throat, voice box and windpipe.  In the lungs – where abnormal suction pressures are at their most intense in the tail-end small airways – this explains, why heavily blood-stained oedema fluid is drawn from the lung into the airways and a horse “bleeds”, he says.

The physics of suction in a horse’s lungs are the same as for a hickey on human skin, but the “sucks” are more brutal and more frequent.  In one minute – 150 negative pressure “insults” – a horse can be sucked to death.  As he writes, “30 strangulated breaths” may be more than enough to kill.

Cook concludes: “Bit-induced asphyxia and its consequences are preventable.”

He urges racing administrators to investigate bitless racing and “update a rule incompatible with equine physiology”.

Removal of the bit, he says, will banish undoubted pain in the mouth and suspected pain in the chest; allow a racehorse to breathe freely; and greatly improve its quality of life.

In addition, he predicts it will reduce the prevalence not only of asphyxia, lung bleeding, and sudden death, but also that of catastrophic and non-catastrophic limb injuries.

Cook reminds us that unimpeded breathing is essential for optimum performance.  Mental and muscular fatigue is a sequel to breathlessness.  Cook implies that metal in the mouth can take the “heart” out of the horse. Weak muscles have disastrous consequences for tendons, joints and bones.  Add in, he continues, the expense of head/neck pendulum interference that prevents a horse from making full use of this crucial energy-saving device.

A rule change to permit bitless racing, Cook asserts, will reduce injuries to exercise riders and jockeys, lengthen the life of racehorses, and improve racing’s public image.

Bit-induced asphyxia in the racehorse as a cause of sudden death. W.R. Cook. DOI: 10.1111/eve.12455
The abstract can be read here

A photograph of a print that hangs on the wall of the Red Lion, a famous old inn in Stockbridge, Massachusetts. It portrays the use of a stopwatch (see rider on left) to time a match race for a trotter. Both horses are portrayed with their their mouths open.
A photograph of a print hangs on the wall of the Red Lion, a famous old inn in Stockbridge, Massachusetts. It portrays the use of a stopwatch (see rider on left) to time a match race for a trotter. Both horses are portrayed with their mouths open.

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11 thoughts on “Bits can suffocate racehorses and cause sudden death, suggests professor

  • November 22, 2015 at 3:27 am

    If you check, you’ll learn that there’s no record of bleeding in the history of the Pony Express. The horses galloped 10 to 15 miles between relay stations, with bits in their mouths. Good thing they didn’t bleed since they were often galloping through hostile territory.

    It’s a very detailed history that documents lots of problems the Pony Express encountered, but no mention of bleeding. So the bits back then weren’t a problem.

  • November 22, 2015 at 5:59 pm

    The only trouble is that if a pony express horse was found dead in the pen it was in they just dragged it out and brought in a replacement thinking nothing of it. I think this researcher is onto something important that could save a lot of horses lives. I can’t count how many times that I have read about a perfectly healthy young race horse just dropping dead after a race. I believe a lot of horse owners are using bitless bridles the way I understand the horses don’t mind wearing them,

  • November 23, 2015 at 12:20 pm

    This research is outstanding and explains so much. Great work Dr Cook. It just makes perfect sense when the biomemchanics involved are explained. Sadly the race industry will be the last to take heed of it, probably never will. Just as they have ignored the research into hoof problems and how they lead to the secondary issues that later cause catastrophic injuries. Why is racing allowed to ignore current research???? They should be funding it!!!!!!!!!!!!!

  • November 25, 2015 at 8:04 am

    On our farm we have used Dr. Cook`s bit-less bridle on our stallion, Slewquero for several years now. He is actually easier to stop and is more responsive in changing of gaits from slower to faster and back again. Directional control is somewhat less effective as he is a very smart horse and sometimes he has figured out that he can evade it at times and go where he wants!

  • November 26, 2015 at 1:02 pm

    The bitless solution shown on the racehorse is an LG Bridle. I’ve used one of those for years on one of my horses and found it to be very effective. Unlike the Dr. Cook’s design (which is a cross under), the LG uses direct turning aids. It also releases very well. This design is also sold as the “Orbitless” bridle.

  • November 28, 2015 at 8:14 am

    Dr Cook doesn’t just blame the bit for EIPH. He also points to the pain that bits can and often do cause – which is the reason horse’s try to evade it. The break of the seal of the lips happens to some degree even when a horse works with its mouth closed but when it opens its mouth wide it does so as a reaction to pain from pressure on the bars, roof of the mouth, the tongue and the corners of the lips. The bigger, harsher the bit and the less able the rider, the worse it is for the horse. When you start to look at horses exercising hard – not just race horses but polo ponies, show jumpers, eventers, carriage and dressage horses – you see many in obvious discomfort with their mouth open. There is also the fact that the bit can trigger the production of salvia and indeed horse people are taught that a wet mouth shows acceptance of the bit and is a good thing. Imagine trying to exercise hard with your mouth producing vast amounts of saliva that you have to swallow or allow to run out and which could easily be inhaled – it would be uncomfortable for us – it’s a physiological nightmare for the horse.

  • December 5, 2016 at 9:37 pm

    So is the problem of the Cook bitless bridle as it never works as planned as it doesn’t release the pressure once you let go of the reins due to the crisscrossed bitless bridle setup. I find the Rambo Micklem muitibridle a better design but it costs almost double the price at $240.00 . Or even better a standard rope halter works every time and costs lesser than $20.00 Thanks Darryl

    • November 29, 2020 at 5:47 am

      I use the Rambo Micklem bridle on a horse that had a tooth break and became very scared of bits. Even after surgery I had to try many bridles and bits. This bridle with the Myler bit that is curved has him riding comfortably again. I would be hard pressed to do a half pass or a canter pirouette in a rope halter. But I can use a rope halter on my quiet QH for trail riding. If he runs away I don’t worry because he will run about twenty feet and decide that is more work than he wants to do:)

  • October 13, 2017 at 6:21 pm

    So when you pull back on the reins of this bit less bridle it doesn’t cut off the horses breathing? It looks like a shank less hackamore, so it puts pressure on the nose. you would think that would hinder the horses breathing.

    • November 23, 2019 at 6:41 pm

      No, it doesn’t hinder breathing, as the nose band sits on top of bone, not the soft tissues of the airways. Also no one should be using reins that hard that it could block nostrils!

      • November 29, 2020 at 5:52 am

        The nostrils run on both sides of that nose bone and a hackamore can restrict their air intake. Hackamores are more severe than most bits when any significant pressure is put on them. I see more runaways with hackamores as the horse panics than I do with bits.


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