The out of form racehorse

                                                 The ‘Out of Form’ Yard / stable 

The ‘Virus’ , ‘Slow horses’ or the ‘Equine Canary Syndrome’ ?



   Firstly the ‘Virus’ . An organism for which there is no treatment, spread by aerosol or droplet infection and which once in an environment such as a stable will spread to all animals that are within a long breath of each. The young and unvaccinated are usually the worst affected. Horses are often febrile ( high temp.), docile and or inappetent (off their feed) for the first 48 hours and then follows varying degrees of secondary ( bacterial) infection with associated coughs and discharging noses. Older horses are less likely to be febrile though. The stables race form then declines for a significant period of time , often 2-3 months before full recovery and form are resumed. The seasonality of racing in Britain combined with a serious viral outbreak may mean a full season is lost in that particular yard.


  Sometimes as ‘luck’ would have it ( or a lack of the same) a particular group of newer often younger horses that enter a yard are simply not possessed of an abundance of natural ability ! Thus apart from the efforts of a few of the ‘old reliables’ the season can be a lean one. With overall winners from horses bred being in the range of 10-20% in Britain it is fair to say that everyone must have a turn at training the slower ones and accordingly struggle to win races.


   However when one bad season is followed by another.... and another, and ill health and other problems seem to be ongoing it is not uncommon to hear whispers of “the Virus” that apparently keeps recurring or just won’t go away. This concept is of course rather ridiculous. As with ourselves once we have recovered from a particular virus our immune system self immunises. If there were a further viral attack then it would most often be another type or variation of the original virus.

But could there be other causes of these epidemic type syndromes of ill health and poor performance ? The answer is of course,Yes !


Often symptoms are vague but seem to be present in the larger proportion of horses in the yard. Poor performance , poor appetite, lower airways ( lung) infections and inflammation, low haematocrits ( red blood cell numbers) , blood stress pictures ( white blood cell differentials) and muscle burn and stiffness are commonly reported across the yard. There can be more specific changes such as neural hyper-reactivity and elevated liver enzymes dependant on the possible causative agent or agents.

Accompanying these changes there is an often reported  increase in the incidence of thick windedness and gurgling ..etc. in the yard. This may be related to specific pathological changes or damage in the respiratory tract or this may just be an expression or symptom of the reduced level of health and fitness of the horses affected.


Often when these situations arise the first complementary tests that are carried out are analysis of feed , soil, and water samples. Here we are considering the first of the two major entry points for possible irritants or toxins. The mouth or oral cavity leads on to a massive moist thin mucosal surface available for the entry of both required and unwanted substances. Therefore checking levels of toxins within prepared feed and for plants such as Ragwort in hay are important considerations. Also a check of feed proportions ( e.g. too much protein or carbohydrate ) and levels of salt and mineral supplementation are important. Having satisfied oneself ( or the relevant professional advisor) that all is well in these departments then let us consider the other orifice or entry point.


These are the nostrils which of course are the entry point to a football field sized area of respiratory mucosa required for gaseous exchange but which is also very exposed to ‘anything’ inhaled.

And whilst on the subject one must also consider that material normally destined for one entry point, ( for example food, saliva and oral bacteria should pass on to the stomach) can and most often will cause problems if they leak into the other. ‘Mouth breathing’ during exercise appears to be occurring more commonly in performance horses and often results in these oral materials being sucked into the airways. Horses are of course obligate nasal breathers unlike ourselves who can breath both orally and nasally at will. On the other hand if air entering via the nostrils is incorrectly drawn into the stomach ( this can occur in horses that have a particular congenital condition referred to as ‘Fourth Branchial Arch Defect’) then mild to fatal gaseous colics can ensue. 


Another important factor to consider is the relative sensitivity of the equine respiratory mucosas to inhaled toxins or irritants? One should in my opinion consider the out of work or resting animal as being reasonably resilient whilst a horse in full training and racing mode is more like the Canary !  Why ? Well it is well recognised that an ‘in work’ horse has a much greater level of lung reactivity or sensitivity than does a resting animal. This state is of course directly related to the stresses and strains being imposed upon these tissues in an attempt to achieve maximum fitness and thence performance. The incidence of orthopaedic injuries is proportionately higher in human athletes in training for the same reason.


Thus once we are reasonably sure that an epidemic viral state or other obvious infectious agent is not the root of our problems then what other possible inhaled irritant substances should we be looking for?

The following is a list of agents, which may, and I stress ‘may’ contribute to states of ill health within a yard.  The list is by no means complete, but it certainly covers the main  ‘suspicious situations’ or areas of concern that I have encountered to date.



Your CHECK LIST for ‘Other Airborne factors’.


Remember respiratory viruses enter at and through the respiratory mucosas . Airborne irritants do the same. Some agents simply cause irritation at the surfaces and others enter the blood stream and have their effects on numerous systems. The potential threat to an individual animal will be in direct proportion to the amount and concentration of the agent that arrives at the respiratory surfaces, the state of health of the individual and the level of training at the particular time. i.e. Already inflamed or hyper-reactive mucosas will obviously be more at risk. 


1) pollens - the most notorious of which is Rape Seed pollen. These are of course seasonal and come via prevailing winds. 

2) fungal - Aspergillus. Found in most stable environments. Levels in both bedding and feed can be assessed and relevance attributed. Tracheal wash results give some indications of levels present in the airways. Control with good stable management and anti fungal disinfection when box is emptied. Make sure animals are away when treatment is being carried out. Follow manufacturers recommendations.

3) dust mites and other stable bugs. Always present and thus concentrations important. Regular bedding changes will usually keep levels at a minimum.

4) bedding / hay - Hay dust is a well recognised irritant.  Soaking hay or feeding outside the stall  in a small open yard can reduce inhalation rates.

5) arena /  menage base - any surface in constant use can interplay with airway surfaces as its components are kicked into the air during exercise. The size of particles and the nature of the compound is important. Sand / dust is less likely to irritate significantly . Synthetic surfaces are often quite inert when initially laid due to their relatively large particle size. With constant use the size will most probably be reduced and thence will be more likely to become airborne and come into contact with mucosas. See manufactures for use by date and then replace. This date will of course be relative to usage. Also quite obviously this factor is more important in an indoor environment where ventilation is poorer.

6) Factories / industry.... Here one can use simple non scientific measurements .. (i) the smell test? If you can smell it ? Then it is reaching your mucosas and your horses. (ii) If there is an asthmatic sufferer on staff are they affected / bothered by it?  OR where available specific monitoring can be performed by environmental authorities . An environmental monitoring unit installed at the stable for 4-6 weeks should supply some useful information one way or the other. Some larger companies / factories have their own mobile units.

7) Agricultural sprays ( mixtures of herbicides and pesticides) ... again one can apply simple tests (i) & (ii) above. Then discuss spraying protocols with farmer / neighbour. Establish buffer zones which need to take into account prevailing winds , make sure you are notified prior to spraying so that barns can be closed or animals removed from barns and gallops. These sprays were not developed for use with animals ( including the human animal).

N.B.  some of these agents are also absorbed through the skin.

8) smoke from fires .  What are you burning ? Smoke itself is an airways irritant. Remember more people caught in house fires die of smoke inhalation than burns. Plastic and other synthetic substances can produce very toxic smoke. Those plastic covers from shavings etc.

9) National pollution -Vehicles etc... see national pollution level maps. This is unlikely to be an issue in Britain where most training is carried out away from the larger industrial / urban centres. In other countries where urban / track based training is the norm at least the playing field is often level. Human health including respiratory can certainly be adversely affected by high levels of pollution.

10) In rare cases past chemical dumps legal or illegal have been found to be still  emitting toxic fumes of danger to both human and equine animals. Check with the relevant authorities.


In the main their are no safe or significant levels recorded for many of these substances with regard specifically to the ‘equine athlete’. Studies have however been carried out in reference to Aspergillus and rape seed.

Likewise the exact mode of action of most of these substances and upon which systems they will impact is unresearched in the equine athlete. In addition quite often there will be more than one irritant factor involved and sorting out the relative significance of each and their possible interactions can be quite a headache !


The best policy therefore is quite obvious and simple.  Where possible avoid  or reduce the incidence or intensity of contact between potentially irritant or toxic agents and your horses mucosas both oral and respiratory. More often though you are simply trying to keep levels of exposure to a minimum. Lets be honest about it ! We live in a more and more toxic world, of our own creation.


As with a human flue epidemic, if 500 people acquire the virus some recover uneventfully, some have secondary complications of varying intensity which in the more serious instances leave life long scars whilst an even smaller number often the very young or very old, will die! Mass exposure to varying irritants can similarly lead to a variety of complications amongst individuals.

Also to consider is that factors 1) - 10) may well potentiate or amplify the effects of a known viral outbreak thus making the consequences in one yard with any of these other possibly irritant factors more severe than one without.


1) - 10) could conceivably contribute to increases in lower airways inflammation / infection and bleeding in the absence of a viral outbreak. Due to the increase in airways  compromise , both upper and lower, the incidence of breathing problems related to both will then increase. It is most important then that before considering medical or surgical intervention for these breathing problems, we should first deal with any ‘airborne factors’, otherwise improvement in race form following these interventions is likely to be  temporary or just plain disappointing.


SUGGESTIONS -

If you are concerned about ongoing yard problems with poor performance then you should

1) Have diagnostic tests performed to eliminate infectious agents, most importantly viral.

2) Work through the above lists of both oral and respiratory toxins or irritants and then eliminate or reduced the severity of any these. Next allow a clear 6 weeks before reassessing.

3) Given that the situation has improved and these other contributing factors have been dealt with, one can then more accurately asses any residual breathing, muscle ( injury v’s metabolic) or other physiological problems ( blood parameters).