The unpalatable truth: Bits are linked to a host of behavioral and breathing issues


The use of the bit can be linked to a host of behavioral and breathing-related problems in horses, writes Bob Cook, Professor Emeritus of Surgery at the Cummings School of Veterinary Medicine at Tufts University in Massachusetts. And, he suggests, racing authorities who assign catastrophic breakdowns to problems with the musculoskeletal system might be missing the root cause.

The growth of knowledge in any field of study is a never-ending process.

In equine medicine it is unsurprising that there is uncertainty and no consensus on the cause of some diseases.

As removal of the cause is crucial to treatment, such diseases are difficult to cure or prevent and there is often a confusing abundance of options for their management.

On the other hand, there is consensus that the cause of many respiratory diseases of the horse is unknown.

Ironically, recognition of a pattern of unknown cause in a group of diseases can be a stepping-stone to understanding.

The family likeness of these “breathlessness-at-exercise” diseases of unknown cause include palatal instability, collapse of the floor of the throat airway (dorsal displacement of the soft palate), collapse of the roof of the throat airway, obstruction of the voice box at one or more cardinal points (e.g., epiglottis, vocal cord, ‘flapper’ cartilage), collapse of the roof of the windpipe, cartilaginous deformity of the windpipe (‘scabbard’ trachea), inflammatory airway disease (equine asthma), exercise-induced pulmonary haemorrhage (negative pressure pulmonary oedema), and sudden death (Cook 2015).

All these are referred to in veterinary textbooks as “idiopathic” – a medical term for diseases of unknown cause [sic].

In the last 20 years, my research has led me to conclude that they are linked by a common cause – the bit.

Two mechanisms explain how the bit obstructs the throat airway, operating singly or together.  First, by preventing maximum head and neck extension at fast exercise. Secondly, by disrupting the lip seal that — in the wild horse — maintains a sub-atmospheric pressure in the digestive part of the throat and firmly approximates the soft palate to an immobile root of tongue when a horse is running.

In so doing, the size of the digestive part of the throat is minimized in order to maximize the size of the respiratory part – the airway. The likelihood of such a causal link has been recently reviewed by Mellor and Beausoleil (2017).

A conservative respiratory rate for a galloping horse is 120 breaths a minute – that is, two full breaths every second. An uninterrupted and maximum flow of air is critical, not just for running but for life itself.

A bullet to the brain or a lethal intravenous injection might kill faster than an obstructed airway but an obstructed airway can be equally lethal.

If the asphyxia is not fatal it will, nevertheless, rapidly cause fatigue of leg muscles and handicap performance.

Exhaustion and lack of muscle tone can be followed by falls and fractures/dislocations or these same problems can arise first and falls follow.

The point is that when racehorse accidents are classified on a systems basis (as a guide for the direction of future research), an assignment to “musculoskeletal system” does not necessarily pin-point the root cause.

Failure of the musculoskeletal system may be secondary to failure of the respiratory system (Cook 2014).

When reading a report that a racehorse incurred a long-bone fracture, by all means consider that a pre-existing microfracture could conceivably have been present that led to a complete fracture during a race.

But consider also that the fracture could have been secondary to asphyxia-induced muscle fatigue.

Whereas microfractures may well occur, they are not as ubiquitous as a bit.

As ‘common things, commonly occur,’ it is appropriate to ask which is the most likely cause – a pre-existing microfracture or a bit?

Furthermore, with regard to future studies on accidents in general, the latter hypothetical explanation lends itself most readily to testing.

In addition to respiratory disease, there are many behavioral problems of the ridden and driven horse that horsemen are all too familiar with and yet are listed as of unknown or uncertain cause and for which effective treatment is elusive, e.g., headshaking.

Other problems, like an open mouth (which leads to a throttled throat – see above), lack of head and neck extension at exercise (another cause of a throttled throat), “bit lameness”, excessive salivation, spookiness, bolting, bucking, rearing and general resistance to training are also common and difficult to treat because their cause is not recognized.

They are often incorrectly attributed to some psychological deficiency of the horse or even accepted as “normal.”

Admittedly, there may be more than one cause of these problems but we should ask, is there one cause that is overwhelmingly more common than any other?  A recent study suggests that there may be.

Sixty-nine behavioural problems in 66 horses were shown to be statistically correctable by removing the bit (Cook and Kibler, 2018).

My hypothesis is that bit-induced airway obstruction causes a family of respiratory diseases and that bit-induced pain causes a family of behavioral problems. To test this idea I recommend a simple therapeutic trial.

When any of the above diseases or behavioural problems are encountered, first remove the bit. For recreational riders this is really simple. They can wake-up one morning and just do it. By the end of the day they will have a happier horse and be on a path to a true partnership, safer riding, enhanced performance and ethical equitation.

Showjumpers can make the same decision, as showjumping rules do not require a bit.

For racing, dressage, Pony Club and other events, use of a bit is mandated.

Yet there is no evidence to support the opinion that bits are necessary for control and safety.

On the contrary, there is ample evidence that a bit endangers the life of both horse and rider.

To retain the social licence and sustainability of horse sports in general, the causes of accidents, injuries and deaths of both horse and rider, have to be addressed.

Bit-free training and racing trials are needed. Bits do not have to be banned. All that is required is that riders and drivers should have the option of choosing between a rein-aid that causes pain, disease and accidents and one that does not.

Once the option becomes available and bit-free benefits are recognized, bits will quickly become obsolete.


Cook (2014): A hypothetical, aetiological relationship between the horse’s bit, nasopharyngeal asphyxia and negative pressure pulmonary oedema. Equine Veterinary Education, 26, 381-389

Cook, W.R, (2015): Bit-induced asphyxia in the racehorse as a cause of sudden death.  Equine Veterinary Education. 28, 405-409

Cook, WR. and Kibler, M (2018). Behavioural assessment of pain in 66 horses, with and without a bit. Equine Veterinary. Education

Mellor, D.J. and Beausoleil, N.J. (2017).  Equine welfare during exercise: An evaluation of breathing, breathlessness and bridles Animals. 7, 41

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17 thoughts on “The unpalatable truth: Bits are linked to a host of behavioral and breathing issues

  • November 14, 2018 at 1:38 am

    Sorry to contradict a vet, But I have been involved with horses as an owner, breeder, trainer and coach for 70 years and this simple Egg butt snaffle Bit is used by riders of all abilities.
    I personally prefer the French snaffle, which has a lozenge in the middle, which I consider to be kinder.

    • November 19, 2018 at 3:00 am

      I AGREE !!! 100 %
      Their comment “”On the contrary, there is ample evidence that a bit endangers the life of both horse and rider.””
      Will ENDANGER many people if their advice is followed by “just wake up one day and remove the bit !!
      I do think there is a small percent of people that will always abuse , in their hands
      any bit will hurt. Too tight nosebands and flash exc……is probably even worse !

      • April 5, 2020 at 11:51 am

        Simply not true. I’ve been converting horses to bitless in show jumping for over 30 years. Every single one of them made the switch within minutes and every single one became a safer, softer horse.

  • November 14, 2018 at 12:41 pm

    Great article. I’m interested to know if leather bitting was tested, but it’s just an afterthought. I’m about to test my mare in a very simple flat leather snaffle, but my presumption is that she will love a mild hackamore or side pull.

    • February 13, 2020 at 7:40 pm

      My mare has been spared from agonizing bit pain for over 20 years now thanks too the Cook Bitless Bridle. Before I switched, after riding, she would work her jaw and roll her eyes back like a shark. She was antsy and jiggy. After I started with Dr. Cooks bridle she was like a different horse! She even became the horse I gave lessons to beginners on. She quickly became more focused and showed more enjoyment in her work. We’re growing old together, I’m 57 and she’s 28 and in spite of my increasing health issues, we still manage to hit the trails, a little slower and not nearly as often but always happy (both of us) and safe.

  • November 14, 2018 at 1:50 pm

    Great research and explanation. Thank you. I have always started young horses bitless and now all my horses remain bitless. I specialise in teaching relaxation and healthy biomechanics for the horse. There is absolutely no need to use a bit!
    I am always hungry to learn more.

  • November 15, 2018 at 8:49 pm

    Great reading

  • November 17, 2018 at 12:53 am

    Great article. Thanks! I am now a Gentle Bitless Horse Trainer, but whwn I started learning how to ride, it’s been on bitted horses. I didn’t like the feeling of that piece of metal in the horses’ mouth from the beginning, so I started searching for alternatives right away. So I’ve found there are people who are riding bitless and ever since that discovery I’ve been riding all kind of horses bitless, I prefer the simple rope halter. God bless you for your research and all the people who show a great example by riding horses bitless for the sake of the horse!

  • February 8, 2020 at 5:39 am

    I too ride bitless my mare is much happier without metal in her mouth, when people say they wouldnt be able to control their horse, I say if a horse bolts a bit won’t stop it and relationship with our horses is about mutual trust not about control which is tantamount to bullying

  • February 8, 2020 at 9:08 am

    Good for you! And your horse! Glad to hear more and more people rides bitless! 🙂

  • February 8, 2020 at 1:28 pm

    The point in the article that there are choices to be made where riders can decide to go bitless to ensure better health and overall happiness of their horse is excellent. Soft hands, riding a bitless, and having a compassionate heart can go along way towards developing a relationship with your horse.

  • February 11, 2020 at 6:30 am

    I use a bit on my 4 year old, but try to keep very light connection, and ride as if I don’t have reigns. I hate that Dressage shows require bits. Needs to change.

  • February 11, 2020 at 6:38 am

    I started using a sidepull one day out of the blue and her performance and response improved. Then I took the reins off and she still listens just fine. Without reins she looked for other cues like legs, seat voice. No more head throwing and she is more relaxed. Bits are useless, cruel, and exist to cause pain and make money.

  • February 13, 2020 at 9:31 am

    The difficulty lies, not in the new ideas, but in escaping from the old ones, which ramify, for those brought up as most of us have been, into every corner of our minds.

    ~ John Maynard Keynes ~

    As someone who has ridden bitless for 30+ years, I can attest to the above quote.

  • February 14, 2020 at 5:33 am

    Thanks Chuck Mintzlaff, you are indeed one of those few people who really understand horses and can make good friends even with the most abused, aggressive, fearful horse. The world is lucky having you.

  • March 2, 2020 at 5:43 am

    It’s like Chuck says: it’s difficult to change ideas and to admit that what you always did is maybe not the best way after all…
    Thank you for the article!


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