C.O.P.D.

Chronic Obstructive Pulmonary Disease

by Dr Colin Roberts, ILPH sponsored vet at the Animal Health Trust (photos courtesy of Bohringer Ingelheim Ltd)

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Respiratory diseases are a common problem in horses and ponies, in fact the most frequently occurring equine medical condition in this country is a disorder known as chronic obstructive pulmonary disease or COPD. This is sometimes known as "heaves", "broken wind", "hay-straw allergy" or emphysema. In this article I shall explore the causes and treatment of this often frustrating condition.

The signs of COPD are variable depending on the severity of the disease. In mild cases the only symptom may be reduced ability to exercise and thorough examination may be necessary to achieve a diagnosis. At the other end of the spectrum, patients may be in a state of distress showing severe difficulty in breathing, with wheezing, coughing and nasal discharge. The disease causes difficulty primarily in breathing out (expiration) and the abdominal muscles have to play a much greater role in respiration than usual.

Because the muscular effort of expiration is increased, it is often possible to see two distinct phases to it in affected horses and this type of breathing is often described as a "double-lift" of the flank in expiration (in fact, all horses breathe out in a two-phase fashion, but in the healthy animal, it is very difficult to discern this by the naked eye). In more severe and long-term cases, the abdominal muscles become enlarged due to the extra work load placed on them, producing the so-called "heave line" along the horse"s flank.

The term COPD is borrowed from human medicine and is somewhat misleading. In medicine, the term "chronic" means not "severe" (as many people believe) but rather "of long duration" or "developing slowly". Whilst this adjective can describe COPD since it is generally a permanent disease once it develops, it is misleading because COPD can arise acutely, i.e. it can occur suddenly and/or severely. In fact equine COPD is very similar in many ways to asthma. Both diseases involve periods of clinical signs that are often separated by intervals of remission when the patient appears to be better.

In the majority of cases, COPD is caused by an "allergy" or hypersensitivity to mould spores found in the horse"s environment. These spores are of respirable size, that is to say, with diameters of 0.5-5.0 mm (1mm is equal to a thousandth of a millimetre). They penetrate the defences of the upper airways and reach the small airways in the lungs. Although one does not usually perform tests to determine the individual species of spores to which a patient is allergic, it appears likely that in the majority of cases there is a multiple allergy to many individual species.

The clinical signs of COPD arise due to the responses of the respiratory tract to challenge by allergens (allergy inducing particles). These responses take three main forms; inflammation of the airway walls, excess mucus production and bronchospasm (narrowing of the airways due to contraction of the muscles in their walls). The net effect of these processes is a narrowing of the airways and reduced capacity for airflow.

Should you suspect that your horse or pony has a respiratory disorder, you should consult your veterinarian who will perform appropriate diagnostic techniques to determine what the problem is. He or she will also be able to advise on specific treatment and this article should be taken as a general discussion rather than a "recipe" for home therapy. As is the case for most allergic disorders, the best way to treat COPD is to avoid contact with the potential allergens. For the majority of horses with COPD, this is best achieved by keeping them permanently out of doors and feeding minimum-dust substitutes for hay, such as "Horsehage" or complete feed nuts. In many cases, however, owners are unable or unwilling to institute such changes in management and the stable environment has to be modified.In many cases, however, owners are unable or unwilling to institute such changes in management and the stable environment has to be modified.

Good ventilation is important in all equine accommodation, but vital for the COPD patient. There is rarely any indication to close the top door of a loose box. The major source of mould allergens in the horse"s stable environment comes from hay and bedding. Even good hay can contain millions of mould spores and horses affected by COPD should ideally be fed substitutes for hay as described above. If this is not possible, then the best quality hay should be fed after soaking it thoroughly in water. Due to the difficulty of soaking a full hay net completely, this generally means submerging the hay in water for some time, often several hours. Whilst there is evidence that this may reduce the nutritional value of the hay somewhat, I have never come across a patient who lost weight as a result of feeding wet hay.

The use of a low-dust bedding is also important for the COPD horse. The best option from the respiratory point of view would appear to be no bedding, which is possible by the use of rubber matting on the box floor. If bedding is used, then a minimum-dust material should be used, such as shredded paper or cardboard. Wood shavings can also be satisfactory for many affected horses, but straw generally has a high mould count. As there is variation in the composition of these materials, the mould content can vary and in any given case it is often a matter of experimenting to find a material that works well. It should go without saying that management of the bedding should be of the highest quality whatever material is used; deep litter is never appropriate for the COPD patient.

Of course, there is limited value in maintaining a horse on a minimum-dust regime if the boxes close by are not managed similarly or if there is a store of hay or straw nearby as spores from these sources are likely to contaminate the affected horse"s air space. Removing the affected animal from the box during mucking out when the dust levels in the air are highest is also important.

Although the long term strategy for the control of COPD should be managemental, there are a variety of drugs which can be used to speed remission, when the horse"s regime is changed and to help during times when management is difficult. It is important to remember that for COPD, these agents are not a cure, merely an aid in the management of a permanent condition. Your veterinarian will be able to advise you on whether pharmaceutical agents are indicated in any given case.

Whilst COPD can cause severe respiratory distress and is generally a permanent condition, many horses live and work normally despite being affected by it, so long as their owners take a responsible attitude and attend diligently to the management of the condition.

Cox the Saddler would like to thank the ILPH for this article.
The ILPH are available at www.ilph.org

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