Undetected respiratory disease - Janet Wescombe
BSc(Hons) HorseHage Consultant

It is estimated that up to 60 per cent of all horses in this country suffer from undetected respiratory disease, a condition which adversely affects a horse's performance and if untreated, can lead to COPD. All healthy animals are born with clean lungs, so what causes damage to their respiratory systems, and what can be done to prevent it?

Respiratory problems can be caused by two main factors - disease and environment. Disease: Infections of the horse's respiratory system can have a serious effect on its ability to breathe efficiently The infections are caused by viruses, such as influenza and herpes, and bacteria including strangles and mycoplasma.

It takes at least a month for the cilia in the horse's airways to recover their full function following a 'flu infection. During this time they will be less effective in removing foreign bodies, so it is even more important for the horse to be in a clean environment. The situation is often made worse because the horse is likely to be stabled for 24 hours a day at this time.

Environment: The effect of the environment on a horse's respiratory system is the most important, in many ways, and luckily is the easiest to control. The stabled horse is subject to constant dust from hay, bedding, feed, rugs, grooming etc, A respiratory infection, or an allergic reaction to fungal or mould spores, or to noxious gases such as ammonia, causes inflammation of the small airways which is exacerbated by a dusty environment.

In humans it is well known that there is a link between respiratory tract infection and allergic respiratory disease. Horses are even more sensitive to respiratory allergens after an infection of the respiratory tract, since the damage caused allows easier access of airborne allergens to the sensitive tissues. Once a horse becomes sensitised, it will remain so for life.

Hay is the single most common cause of fungal spores, and a horse may inhale millions of spores with every breath. Even "clean" hay will be contaminated. It has been said that one kilogram of top quality hay contains as many spores as there are people on the earth! Soaking hay will not remove the spores, and they will become airborne as the hay dries.

Other foodstuffs such as cereals can also be a source of spores. Bedding, particularly straw, contains spores and any bed which is not well managed can lead to a build up of gases. In a horse which is sensitised to fungal spores the airways do not return to normal, and substances produced in the body cause inflammation and more mucus production, all of which further reduce the diameter of the small airways. Thus it is harder for the horse to breathe and all the air may not be expelled.

The alveoli may over-inflate and become damaged, releasing chemicals which compound the problem. This condition is known as emphysema, broken wind, or chronic obstructive pulmonary disease (COPD).

A horse with severe COPD will show obvious symptoms such as coughing, a nasal discharge and forced, rapid breathing. There is also the characteristic "heave" line along the sides of the horse, caused by it having to use extra muscular effort to empty air from its lungs. A horse with severe COPD is struggling to breathe even at rest and is not able to perform at all - but even a mild case will affect performance. Once a horse has a respiratory problem, it is important to remove the causes.

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