Sudden 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.
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.
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.
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