Q&A with Dr. Robert Cook, Creator of ‘Dr. Cook’s Bitless Bridle’ (Part 2)

HR mug shot with Carlos

Robert Cook, FRCVS, PhD graduated as a veterinarian in 1952, from the Royal Veterinary College, London UK. Subsequently he earned a Fellowship of the Royal College of Veterinary Surgeons and gained a PhD from Cambridge. Apart from six years in practice and eight years as a senior scientist at the Equine Research Station of the Animal Health Trust, Newmarket, UK, he has been a clinician, teacher and researcher at university schools of veterinary medicine in the UK and USA. He was appointed Professor of Surgery Emeritus of Tufts University, Cummings School of Veterinary Medicine in 1994. His focus of research is diseases of the mouth, ear, nose and throat of the horse. He became Chairman of BitlessBridle Inc. in 2000.

(This post is a continuation of Part 1 of my Q&A session with Dr. Cook.)

As a vet and researcher, what type of damage have you observed that resulted from the use of a bit?

Some short questions require book-length answers and this is one of them. To answer briefly, the types of damage to the horse can be described as physical, mental, behavioral, and physiological, though there is considerable overlap between all categories. Likewise, ‘damage’ to the rider can be described as psychological, economical and medical.

Effect on the Horse:

a) Physical damage: The direct mechanical damage that one or more metal rods can inflict on the sensitive tissues of a horse’s mouth includes:

  • lip sores, cuts and sarcoids from longitudinal stretching of the lips
  • laceration and amputation of the tongue
  • gingivitis from pressure on unerupted wolf teeth in the lower jaw
  • a sore mouth from bruising of the gum over the bars of the mouth
  • bruising of the roof of the mouth
  • bone spurs on the bars of the mouth
  • star fractures of the bars and the shedding of dead bone (sequestra)
  • erosion and shedding of the first cheek tooth in the lower jaw
  • chip fractures of the first lower cheek teeth
  • periodontal disease; and
  • damage to the jaw, from fractures and osteomyelitis.

To read my article on bone and dental damage, click here.

EVJ Fig 2  A204016 bevel, square edge, buttress

Fig. 6. The first cheek tooth in the lower jaw shows an example of the dental damage that occurs when a horse repeatedly grabs the bit and erodes its grinding surface. The bit has also been pressing hard against the front edge of this tooth and flattening its normal ‘prow.’ Such a horse may well have been labeled as a ‘puller’ and been said to have ‘leaned on the bit’ or to have had a ‘hard mouth.’ (Specimen photographed courtesy of the American Museum of Natural History)


Fig. 7. Close-up of the bars of the mouth. The canine teeth are on the right of the picture and the first cheek teeth on the left. The lower bar shows several large bit-induced bone spurs and the other bar shows one smaller spur. Lesions like these can be likened to ‘splints’ on a horse’s shin but are far more painful. (Specimen photographed courtesy of the American Museum of Natural History)

b) Mental damage: This includes acute pain, chronic pain and fear. Acute pain is inflicted by the bit during the generation and maintenance of all the lesions listed above. Chronic pain is the neuralgia that daily use of the bit sets up in the trigeminal nerve (tic doloureux), so often responsible for head tossing, muzzle rubbing and other signs of the headshaking syndrome. Fear is the mental stress, nervousness, apprehension, shying and spookiness triggered by the anticipation of pain.

c) Behavioral damage: The pain and fear of mental damage manifests itself in a hundred and one different ways in the ridden horse’s behaviour but also in (unwanted) behavior prior to and after riding. Examples of some of the more dangerous under-saddle signs include bolting, bucking, balking and rearing. A more comprehensive listing is available here and the full text of this article on the prevention of accidents is available here.

58 controlled experiments were carried out between 2002 and 2008, in which riders compared the ridden behavior of a horse in a bitted bridle with that in a crossunder bitless bridle. Using a checklist of 82 possible signs of pain and distress, the sign most frequently eliminated by removing the bit was of a horse that “hates the bit” i.e., chews on the bit. All horses showed markedly fewer signs of pain and distress when bitless. The summated numbers were bitted 1643 and bitless 202, an overall improvement of 88%. The median number of pain and distress signs that each horse exhibited when bitted was 24 – when bitless 1 (unpublished material).

Most of the behavioral signs of pain result in reduced performance. A different 2008 experiment compared bitted and bitless performance. Four riders that had never previously used a crossunder bitless bridle, rode four horses that had never before been ridden in one. In the first four minutes of removing the bit (in the second ride of a simple dressage test) they increased their scores by an average of 75%. Their score changed from a bitted average of ‘quite bad’ (3.7) to a bitless average of ‘satisfactory’ (6.4). To read the peer-reviewed article click here and for a video of the experiment click here.

d) Physiological damage:  The bit triggers digestive responses when what are needed in the exercising horse are respiratory, cardiovascular and musculo-skeletal responses. Essentially, it triggers a conflict between eating and exercising. The physiological requirements for eating include a head down position, quiet breathing, an open mouth, tongue and jaw movement, salivation and swallowing. For exercising, the requirements include a raised head, rapid breathing, sealed lips, a closed mouth, an immobile tongue and jaw, a relatively dry mouth and no swallowing. A young horse at liberty in a field, interchanging between grazing and playing, can switch between these two requirements effortlessly and smoothly. Too often, the same horse when bitted and ridden presents a very different picture. Its lips are parted by the bit and its mouth may, at intervals, be frankly open. Tongue and jaw movements may be prominent and salivation may be so effusive that saliva drools from the mouth and foams. As a result, breathing is made difficult and the intake of oxygen reduced, triggering a cascade of problems affecting the lungs, legs and heart.

The anatomical ‘damage’ in the throat that sets all this in motion can be best understood with the help of the diagram in Fig. 8. The bit breaks what should be an airtight-seal at the lips and a very necessary oral vacuum is eliminated (Figs 9-11). The head and neck may be flexed, so the soft walls of the throat are flaccid. Under these conditions, aggravated by tongue and jaw movement and even by actual swallowing reflexes, the soft palate gets sucked upwards during rapid inhalation and obstructs the throat (Fig. 11b). This, in my opinion, is the cause of dorsal displacement of the soft palate (DDSP), a physiological scourge of the bitted horse. Again, in my opinion, DDSP is the cause of bleeding from the lungs, the so-called exercise-induced pulmonary hemorrhage (EIPH) better named as negative pressure pulmonary edema (NPPE). Together, DDSP and NPPE, these two side effects of the bit, represent a multimillion dollar problem for the racing industry, currently unsolved by Salix. To read my article, “What causes soft palate problems and bleeding in racehorses?: The answer is on the tip of the horse’s tongue” click here and click also on the two links at the end of this post.

breathing & swallowing

Fig. 8: Showing how the soft palate and cartilages of the voice box act as switch plates allowing the throat to be configured for either exercising or eating (rapid breathing or swallowing). To simplify the diagram for the purpose of emphasising the changes in the throat, air space is shown in the mouth, the oral part of the throat and the esophagus (gullet). This space is severely limited when grazing and eliminated when exercising (see Figs 9 – 11)


AC = arytenoid cartilages (‘flappers’) of the voice box (larynx)

E = epiglottis

LP = laryngopharynx (the food channels on each side of the voice box that enable a horse to graze yet still breathe quietly)

NP = nasopharynx (the respiratory part of the throat)

OI = ostium intrapharyngium (a ‘button-hole’ in the soft palate, into which the voice box fits like a grommet except when swallowing)

OP = oropharynx (the oral part of the throat)

SP = soft palate


Fig.9. Anatomy of the head, showing the configuration of the throat for quiet breathing. The throat serves two masters, breathing and swallowing. For breathing, the size of the respiratory part of the throat (nasopharynx) is maximised at the expense of the oral part of the throat (oropharynx). The double-ended arrow, depicting the airway, has its front end in the throat and its back end in the voice box (larynx).


Fig, 10. The same diagram as Fig. 9 but showing the sealed lips that, after a swallow, enable the running horse when bitless to create a vacuum in those compartments shown in red.


Fig. 11a. Normal configuration of the throat for running in a horse at liberty. The poll is extended, the throat is stretched, and the soft palate is ‘vacuum-packed’ on the root of the tongue and around the voice box. There is an airtight seal at the lips and between the two parts of the throat.


Fig. 11b. Abnormal configuration of the throat when running in a bitted bridle. The bit (yellow dot) has broken the lip seal, allowing air to enter the oral part of the throat. The soft palate is unstable and, in this diagram, is shown in an elevated position that is only appropriate to a phase of swallowing. The airway is severely obstructed at the junction of nasal cavity and throat (red dots).

Apart from the above conflict between eating and exercising there is another major conflict in the bitted horse between breathing and striding. At liberty, the cantering horse takes one stride for every breath. There is a synchrony between the two, called respiratory-locomotory coupling. . But when a bit interferes with breathing this synchrony can be lost. From 82 signs of pain and distress eliminated by removing the bit in the controlled experiment cited above, 34 (41%) were signs that in one way or another impacted a horse’s stride and way of going. The signs ranged from the regrettable, e.g., lack of finesse and reluctance to change leads) to downright dangerous, e.g., stumbling, freezing, bucking, rearing and bolting.

The 82 questions on which the above experiment was based did not include the catastrophic accidents that occur on the racetrack as the result of bit-induced shortage of breath and premature fatigue. Bleeding from the lungs and the appearance of blood at the nostrils or in the windpipe is only the outward and visible sign of a much more serious inward disaster. Bit-induced asphyxia causes massive waterlogging of the lung (pulmonary edema). That red blood cells and edema fluid gets sucked into the small airways of the lung is only one effect of this problem. Not only is a racehorse unable to obtain all the oxygen it needs for running due to the obstruction in its throat but also, because the lungs become waterlogged, it is unable to fully absorb the oxygen it does get. So a racehorse builds up an oxygen debt and is unable to prevent a build-up of carbon dioxide. The heart muscle can no longer circulate fully oxygenated blood to the muscles of the legs, nor to the muscles or respiration, and may even be short of oxygen itself. Adding insult to injury, the heart has to work harder to pump blood around the body to its lungs and legs because of the resistance to circulation imposed by congestion in its lungs. Likewise the work of breathing is increased for the same reason, as the lungs are no longer compliant. Little wonder that a ‘bleeder’ (99% of racehorses are affected to varying degrees) has difficulty in breathing and striding. Premature fatigue, exhaustion, breakdowns, falls, and fractures may follow. The end result of bit damage can be sudden death or euthanasia.

To sum up, the bit damages the digestive, respiratory, nervous, cardiovascular and musculo-skeletal systems.

Effect on the Rider:

a) Psychological ‘Damage’: What many riders describe as ‘bad’ or ‘unwanted’ behaviour on the part of their horse, and for which they may blame their horse, is generally normal behaviour, albeit inconvenient and even dangerous for the rider. Mostly, it is a normal response to pain and fear, largely bit-induced. From the above controlled experiment, not more than 12% of the signs of pain and distress were caused by some factor other than the bit. The 88% bit-induced behavioural responses are frequently the cause of much rider unhappiness. This is expressed in a slew of emotions from self-doubt about their riding skills, disappointment, frustration, reluctance to ride, fear, and even anger with the horse, to a state of mind in which the rider is ready to sell the horse or simply give up riding altogether.

b) Economic ‘Damage’: The staggering ‘cost’ of the bit to the racing industry has already been mentioned but trail riders and pleasure riders also incur bit-related expense for rehabilitation and replacement. For riders who train, compete and sell horses, the cost of poor performance can be considerable. To see a cost/benefit comparison for a bit and bitless rein-aid, click here.

c) Medical ‘Damage’: Horse riding is recognized by insurance companies as being more dangerous than motor cycling. Bit-induced accidents, which are frequent, cause injuries ranging from broken collar bones to broken necks and sudden death.

For a summary of the benefits of the crossunder bitless bridle for both horse and rider, click here.


To read Part 3 of my interview with Dr. Cook, click here.

For more information about Dr. Cook’s Bitless Bridle, visit his website.


Hi! My name is Casie Bazay. I'm a mom, a freelance writer, and a certified equine acupressure practitioner.

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