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The coughing horse

Whilst deep down most people know that what we think of as “flu” in humans is probably just a common cold, many people still cling to the notion that all coughing horses have “a virus”.

As vets we probably deserve some of the blame for this belief, as all to often we will refer to a non specific, “virus”, as the agent implicated in a respiratory tract infection, thereby elevating this vague entity to mythical status. Although as vets, we know who the usual suspects are, and can, with blood tests determine who is actually responsible; in most cases it is only necessary to know that the infection is viral in order to treat the horse appropriately.

The usual suspects

The greatest proportion of horses with “a virus”, have an Equine Herpes virus infection. Less commonly Adenovirus and Equine Rhinovirus are implicated. Fortunately due to mandatory vaccination Equine influenza has not been a serious problem in recent years.

Equine herpes Virus EHV

EHV has several forms including a type that can cause abortion, and a paralytic form. In common with Herpes in humans and the other Equine forms of the virus the, respiratory Herpes virus infection can remain dormant until times of stress. This can lead to a pattern of disease that many will recognise; – recurrent bouts of coughing and lack of energy. The stress that induces the recurrence of disease might be hard work, but often the environment in which a horse lives, can trigger relapses- dust irritation cold wet conditions, changeable weather.

“Environmental” coughs

The misconception, that all coughing horses have a “virus” may also have its roots in the assumption that because we get coughs and colds over the winter, our horses will too. If we look at this notion the flaws in it as a hypothesis rapidly become apparent. The main reason that respiratory disease is rife in humans in the winter, is that we spend most of our time in the winter cooped up together, thus allowing any infections to spread rapidly throughout the population. Although horses do get shut up together they tend to be shut up as discrete groups, i.e. on separate yard. The mixing of different discrete groups within closed environments that happens in humans i.e. at schools, at work, at parties etc, doesn’t happen as much with horses. Horses on the other hand, do spend prolonged periods in environments conducive to coughing. Stables. Very few houses these days have anything like the levels of dust and allergens that one finds in the average stable. Most stables will have high levels of dust from bedding, hay and dried mud, all of which can irritate the airways. Add to these irritant particles, the fungal spores and pollens from hay and straw which cause allergic airway disease and one has an environment in respiratory disease would appear to be inevitable. Although many of the coughs that we are presented with over the winter do have an infectious component, more often than not it is an infection that is secondary to irritation of the airway caused by environmental problems.


In the majority of coughing horses, diagnosis can be made by a normal clinical examination and by studying the history. Auscultation (listening using a stethoscope!) of all of the airway is obviously very informative but in some cases viewing the airway using a flexible endoscope may be necessary to clarify the true cause of a cough. Collection of airway secretions via a catheter passed through the endoscope can be particularly useful in differentiating the causes of respiratory problems arising in the lungs. Analysis of blood can add further useful information.

Prevention of airway disease in the winter

Directly and indirectly the environment is crucial to the respiratory health of our horses in the winter. The allergic horse or pony being particularly susceptible, tends to benefit from a higher level of attention to his environment, with washed hay dust free bedding and good ventilation. However we should strive to keep all stables as free from inhaled irritants and allergens as possible. I recommend Hoovering or pressure hosing stables, to remove accumulated dust from all surfaces, especially tops of walls and rafters. The difference in air quality following a thorough cleaning is very evident. Having created with a nice environment, good ventilation and careful selection and treatment of bedding and fodder should prevent the build up of dust in a stable. Where circumstances allow 24 hour turnout should be considered- it is after all the horse’s natural environment!

The use of drugs and other preparations in many horses is necessary, but should not be regarded as a substitute for good management. Most drugs and supplements require regular dosing but some of the prescription drugs used for allergic conditions can be given “to effect” of “as required” and a clear understanding of when to dose is essential to ensure efficacy and to keep doses to a minimum.

Vaccination against Equine influenza has proved its value in the reduced incidence of Equine flu in the last decade. In my experience I have found that vaccinating against Equine Herpes virus, reduces the incidence of “virus” infections, and recommend it especially for horses that get a “virus” every year.

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