The Winds have changed.

The Winds Have Changed !

Overview - of an apparent  upsurge in the incidence of breathing problems amongst equine athletes :

An INFORMATION ARTICLE  for  thoroughbred owners, breeders  and trainers.

It used to be all about ‘soundness of limb’ when racetrack and stable conversations centred on sore shins, bowed tendons and chipped knees.

Nowadays it would appear that the terms ‘wind problem’ or ‘breathing problem’ are very much centre stage and this because of what appears to be an escalating incidence of ‘ breathing problems’ amongst equine athletes! So what is going on? Is this something new or are we just  more aware of these problems nowadays ? What should we be doing?. These are questions often asked by those in the industry!

Extremely influential equine racing teams are nowadays using either tongue ties or nosebands on ever increasing numbers of their competitors. Even as a ‘precautionary measure’ this certainly  indicates both a significant and increasing degree of concern! We hear constant reference in televised race coverage's to horses both winners and losers having breathing problems or having had surgery for breathing problems. Also comments such as “can’t hold him up as he needs a good pace or he’ll choke”, “Needs good ground because of his breathing problem”, “needs plenty of racing ( sharp gallops) because of a little breathing problem” are common. Make reference to any of the following -   gurgling, thickwinded horses, breath-holding, ‘stoppers’,horses needing oxygen after a race, pre-race ‘shiver and shakers’, boiling over , or ‘non triers’ in front of any horse trainer anywhere in the world and I can guarantee they will not be smiling !

So .. What is going on?  What theories are out there? What should we be doing?

Firstly we should consider the relevant information available today. Information with regard to the mechanical dysfunction's, incidence , surgical treatments and possible causes of these breathing problems. Then more importantly take a look to the future when hopefully we will be able to prevent or at least reduce the incidence of these problems prior to the need for surgical intervention.

‘Breathing problems’ can emanate from dysfunction's of the lungs ( lower airways) and or the throat ( upper airways). Most but not all of the present day discussions re ‘breathing problems’ are in reference to ‘throat problems’.

Now with regard to the equine ‘throat’, it is important to realise that in general the throat can be split into two anatomically distinct areas. Firstly the ‘pharynx’, which is a tunnel or cave like structure approximately 20cm in length. Air enters the pharyngeal cave from the fixed cartilaginous nasal passages and exits through a set of gates at the top of the windpipe on its way to the lungs (lower airways). The pharynx collapses during swallowing to prevent food entering the windpipe but should not collapse during breathing exercise. The gate like structure at the junction of the pharynx and windpipe forms the second part of the throat and is referred to as the ‘larynx’. This gate also closes or collapses for swallowing and opens during breathing.

The throat  has three basic functions. Eating, breathing and singing ( voice production). The three functions are interrelated and the larynx and pharynx play a part in all three.

It is also important to understand that as a species horses are obligate nasal breathers. This means a horse should only take air via  its nostrils, unlike ourselves who use either our mouth or nose as an entry point. However in an emergency or at times when the nasal route is not adequate, a horse can elect to take some ‘emergency air’ via its mouth.  Now this sounds like a sensible system... BUT... air entering through the mouth is both less efficient and is usually contaminated. The contamination consists of saliva, food material and oral bacteria which will invariably be sucked into the horses lungs resulting in an increase in the incidence of  inflammation and or infection.

In the last 30 to 40 years it appears that there has been a significant increase in the incidence of breathing / throat problems in racing horses. Why do we suspect this? Just put this question to any trainer, rider or veterinarian in any racing country around the globe who has been in the industry long enough. Most agree! This phenomena is reported world-wide in thoroughbred , standardbred and racing arab breeds. The actual incidence is still unknown though, as opinions on the significance of both diagnostic protocols and the presence of symptoms in the young, still vary. This increase is however with reference to problems of the pharynx not the larynx. Recent surveys suggest that laryngeal problems are no more common than they were 30 years ago.

Problems of the pharynx are often referred to by using terms such as gurgling, soft palate, thick winded ( inspiratory and expiratory noises), breath holding, stoppers, chokers.. etc

These problems may be temporary or intermittent and are often first noticed after a period of airways infection or a cold / virus .

In young horses these problems are often thought of as being an ‘immaturity’ and thence something they will probably ‘grow out of’. More recently canvassed opinion suggests that a percentage certainly do recover but a bigger percentage probably learn to avoid airway collapse by, in  racing terminology, learning to ‘look after themselves’. They often refuse to work or race to their ability and thence shield themselves from the rather uncomfortable sensations of partial airways collapse and asphyxiation. Unfortunately this often means that they will show little to no symptoms of their dysfunction / problem. This then becomes a diagnostic dilemma for all concerned.

The major physical dysfunction of the pharynx ( pharyngeal dysfunction) occurs when a horse elects to use it’s ‘emergency air supply’ ( mouth breaths) during exercise. This usually occurs in response to an inappropriate partial or complete collapse of the pharynx which most often occurs in association with maximal effort. The primary physiological dysfunction that results is that of a less than optimal supply of oxygen. The secondary dysfunction is invariably an increase in the incidence of lower airways problems due to contamination of the lungs with oral material.

The most common mechanical methods used to discourage pharyngeal dysfunction ( mouth breathing) are

                                   nosebands - to keep the mouth closed

                           and tongue ties - to reduce tongue movement within the back of the mouth. The tongue and soft palate when pressed together form a seal referred to as the oropharyngeal seal which stops air passing through the back of the horses mouth. To break the seal the horse must be able to move the back of its tongue about.

However it is important to realise that most horses can still take some air through their mouths even with both these aids in place.

The other possible scenario is that having discouraged the use of their ‘emergency oxygen supply’ with these aids, the horse will then not choose to put itself in a compromising position and will thus avoid maximum effort. In racing terminology this horse is often referred to as a ‘non-trier’. In the horses defence they are not ‘dumb animals’ and are thus unlikely to willingly put themselves in an extremely stressful situation given the choice. They may ‘run into a wall’ once but are unlikely to do so again at their next outing. How many horses win a very tough race one day and the next time out go to water before the race ( pre race nervous behaviour ) prior to a dissapointing performance ? These often never race up to their previous mark again?

Studies have shown that the most common dysfunction that encourages horses to go for their emergency air supply occurs when the floor of the pharyngeal cave or airway collapses upwards. The floor of the pharynx  is formed by the soft palate. As the palate rises into the airway the airflow is lessened akin to the effect on the flow of water through a hosepipe as the pipe is kinked. In the UK the most common surgical procedure utilised to discourage mouth breathing is that of hot firing of the soft palate. Firing or cauterising the palate results in the formation during healing of scar tissue. The palate or pharyngeal floor is then stiffer and less able to rise into the chamber. Palates are sometimes cauterised a second and third time. A less common but more direct method of tensing the palate is to perform a  procedure refereed to as a palatoplasty. This technique is however technically more difficult to perform and is therefore less commonly utilised. These days a double tensing palatoplasty refereed to as a MAP ( Maximum Airway Procedure) is more popular. Palatoplastys can also be performed over previously cauterised palates as long as scarring is not too severe. The reverse is also possible.

So where does all this lead us?

It would seem that over the last 30-40 years the pharyngeal airways or caves of racing horses of all breeds have been collapsing more frequently. Therefore one could assume that for some reason or reasons they have become more collapsable. The direction of surgery and indeed the success of surgical tensing or stiffening procedures adds support to the idea that these tissues have become abnormally loose or flaccid.

Now if we look at the anatomy of the throat we find that there are three very important types of tissues that play a part in opposing this flaccid state.

Firstly there are muscles that either  directly tense the palate or that pull on broad sail like  tissues, flattened tendons, which likewise increase tension. Secondly there are the nerves that control these muscles and tendons which are obviously equally important .

Thirdly the pharynx has a significant mesh of connective tissues ( collagen and elastic fibres). The most significant elastic structures are present in the soft palate These also oppose airways collapse.

So could there be a problem ( degeneration) of any of these three elements?

The possibility of muscle damage or myositis was first  suggested some 30 years ago. Repeated studies have ruled this out as a significant factor.

Nerve damage similar to that which causes most of the problems of the larynx was also hypothesised. In The early 80’s a group of New Zealand vets carried out a similar investigation on the pharynx to that which they had previously carried out on the larynx and came up with a negative. Very recently US veterinarians again tried to implicate the  nervous system in the more commonly occurring forms of pharyngeal dysfunction but it would appear that their results were similar to those of the previous study.

Then what about the third group of tissues. The connective tissues. Could these be damaged?

Yes ! . Every time a horses is reported to have ‘pharyngitis’ ( inflammation of the pharynx) and this is quite common particularly amongst the young, it is likely that  enzymes referred to as proteases, some of which the horses own body produces during inflammation, could be destroying a proportion of these tissues. Fluids that are expectorated ( coughed up) from the lungs during lower airways infections are often full of these digestive enzymes. These will no doubt cover the lining of the pharynx prior to exiting via the nostrils or being swallowed. Invading bacteria ( infections) can also produce these enzymes as part of their invasive mechanism.

What about normal healing processes which should occur after inflammation and infections have settled?

Well collagen can be replaced during healing but elastic tissue is unfortunately  not . When elastic fibre numbers are reduced tissues will tend to become flaccid and sag. And we who are getting on in years are obviously very aware of this process!

Then has anyone investigated this possible scenario / hypothesis?

No ! apart from a limited study carried out in 1993 with regard to the elastic components of the equine pharynx . During this investigation significant degeneration of these tissues, in sometimes very young animals, was noted  but no conclusions were drawn. At the moment their is no way of quantifying the amount of elastic tissue in a pharynx and therefore no way of saying what is or isn’t adequate.

How could the apparent increase in the incidence of pharyngeal dysfunction over the last 40 years tie in with this degenerative process?

Viruses have been continually changing over the last 40 years and some species may now have a greater pathogenic or destructive effect on connective tissues. In addition it would be ignorant of us to suggest that bacterial populations had not changed significantly during this period of time particularly given our rather zealous use of specific groups of antibiotics. Again different bacteria will vary in their ability to destroy tissues during infectious processes. These newer bacteria may be more destructive. In addition the incidence of another entity referred to as ‘airway hyperresponsiveness’ , which most commonly occurs in young horses, has likewise been on the increase. This hyperresponsive state is often associated with chronic inflammation of airways  which can trigger an increase in production of destructive enzymes. Interestingly this syndrome in young horses appears to parallel the increased incidence of asthma amongst young human animals, in which hyperresponse airways play a significant role.

How could we investigate these possible causes?

Specific equine elastases have already been isolated and identified. Veterinarians often take samples of fluid from horses airways during training or whilst the animal is ill. During infectious or inflammatory processes levels of destructive enzymes could be measured to gauge possible deleterious effects on connective tissues. This would be of most interest in young animals which have less effective immune systems.

Could there be other causes?

Certainly. As we have seen several possible causes have already been eliminated . There are other investigations being carried out away from the ’flaccid tissue’ concept. Most of these theories have however resulted from observations made following the surgical severing , removing or  otherwise interfering with ostensibly  ‘normal tissues’.   

Could this problem be related to breeding?

Very unlikely ! Laryngeal problems which we know do have an hereditary element have not increased significantly in the same period of time. In addition all three breeds of racing equines are affected. It would  also be very unlikely that any individual stallion would have progeny completely free of symptoms of pharyngeal dysfunction.

Thus I would suggest that breeding warnings such as those that apply for horses with significant laryngeal weakness or paralysis should not apply for horses with pharyngeal dysfunction.

How do I know if my horse is suffering from pharyngeal dysfunction?

Diagnostically where a breathing problem is ‘laryngeal’ the use of an endoscope either standing or on a high speed treadmill is very useful. However where the pharynx is concerned the most important tool is an adequate history i.e. what is happening during exercise and racing and this includes the horses race and work associated behaviour. Endoscopy performed in either the standing or treadmilled horse are very much aids to diagnosis or ‘diagnostic aids’. The dysfunction may or may not be apparent whilst exercising on a treadmill. Other horses will refuse, as they do on a racetrack, to exercise at maximum output leaving again an adequate history as the main means to diagnosis.

How important are the noises they do or don’t make?

To begin with we should state the obvious. These animals are competing in galloping races not Eurovision. They are athletes not opera singers. As previously stated the throat has three functions. Certainly an abnormal voice may occur in association with an airways dysfunction but the noise is not the dysfunction. The reduction in air supply is. We also now know that in many cases of airways dysfunction there are no abnormal noises reported. Equally to regard the animal as ‘fixed ‘ after either rest, medical treatment or surgery purely on the basis of noise reduction or elimination can be very misleading.

Better to asses the horse from a performance perspective and also on its attitude to work. A horse that is getting plenty of air will be both inwardly relaxed and at the same time will have a positive attitude to its work. Horses with competent airways  enjoy their  racing and are willing competitors!

What should we be doing in the future to try to reduce the incidence of this problem?

It does appear that there is an ever increasing incidence of airways dysfunction involving the pharyngeal region of the equine athlete.  Surgeries are certainly reducing to some extent the impact of these dysfunction's. However prevention should be our ultimate aim and to this end all potential causes have to be investigated excluding those that have already been eliminated. More specific investigations into the potentially destructive influences of chronic inflammatory or hyperresponsive airways and the invasive mechanisms of more recently encountered viral and bacterial organisms need to be carried out. Then and only then can we talk about preventative strategies.

In recent times a ‘cloud of confusion’ appears to have surrounded the subject. Amongst professionals there has been an understandable concern, when asked to comment on a syndrome that has been referred to as both ‘vague and multifactorial’, that one may be ‘wrong’ and thence be providing misinformation to the public.

Personally I prescribe to the notion that being wrong is as important as being right.

Originally published in Pacemaker UK