Dr. S. Davidson, BVMS, MRCVS at the Sussex Equine Hospital discusses Chronic Obstructive Pulmonary Disease in this feature.
Chronic Obstructive Pulmonary Disease (COPD) is a frequently seen disease that horses can suffer from that is also known as Recurrent Airway Obstruction (RAO), ‘broken wind’ or ‘heaves’. It is a chronic condition often diagnosed following a horse becoming wheezy, developing laboured breathing, coughing and occasionally accompanied by a nasal discharge.
The cause of COPD is an allergic reaction to allergens in the air such as dust, mould or fungal spores that are usually completely harmless, similar to asthma in people. The allergens pertaining to COPD mean that it is often a disease affecting horses that eat hay and are bedded on straw. They enter the horse’s lungs during normal respiration and the horse’s hypersensitive immune system overreacts.
The lungs become inflamed which causes the airway to narrow and mucus production to increase as a response. This results in the clinical signs we see mentioned above. It is also where the term ‘heaves’ comes from. The narrowed airways mean the normal respiratory muscles need to recruit help from other muscles such abdominal muscles. As these begin to work overtime, they grow in size and produce ‘heave’ lines seen horizontally on the belly.
Diagnosis of COPD is usually based on a thorough clinical examination, history and occasionally an endoscopic examination of the trachea, where samples are taken and analysed.
While most COPD cases are diagnosed once a horse starts struggling with exercise or coughing, some horses will present in acute respiratory distress. The horse may be nostril flaring, standing with the neck extended, breathing rapidly and sweating and it can be very distressing for owners to witness. In these cases, it is very important that owners remain calm, take the horse slowly and quietly outside to fresh air and call your vet immediately.
Treatment is based around minimising exposure to allergens and careful management. As an adjunct, medications can be used, but a lot of horses will improve with management changes alone. Improving your horse’s air hygiene is first and foremost to keep them happy and healthy, while maximising their athletic potential. However, it is important to note that acute respiratory flare-ups can be very serious and on the odd occasion, fatal.
A life in the field is the ideal management technique for horses suffering with COPD but this is not always practical. If your horse must be stabled sometimes or all the time, the following may help.
- Minimise dust and maximise air hygiene in the stable.
- Soak hay (60 minutes) to remove dust (any longer and the soaking will reduce carbohydrates) or feed a low-dust alternative such as haylage.
- Feed from the ground to encourage mucus drainage. In the wild, a horse will graze for up to 20 hours a day and having the head lower helps mucus to drain from the lungs. However, in domestic life, horses are often fed from haynets, buckets or mangers which can mean that mucus builds up.
- Bedding should be as dust-free as possible. Rubber matting with paper- or dust-extracted shavings is the best option. Rubber matting is expensive to install but, in the long run, will minimise veterinary bills from repeat visits! In extreme cases, rubber matting can be used on its own and washed daily.
- Good ventilation inside the stable is vital.
- Managing all horses in the stable block to help the individual with respiratory issues is very important, although can prove tricky on a livery yard. Making sure the affected horse is outside for mucking out and sweeping (and for a short time after to allow dust and spores to settle) will make a big difference.
As mentioned before, not all cases can be resolved fully with management. There are four broad categories of drug that can be employed to help.
- Bronchodilators which help to open up the airways and allow the horse to breath more easily.
- Corticosteroids which reduce lung inflammation and decrease the severity of the hypersensitivity reaction.
- Anti-histamines also reduce the severity of the hypersensitivity reaction and are best given pre-emptively.
- Mucolytics can help to make the horse’s mucus less viscous and, therefore, easier to clear.
These medications can be delivered intravenously or using an inhaler or nebuliser as a gas directly into the lungs. As with any medication, if it’s being used in a horse that is competing racing, withdrawal times should be carefully observed.
A variation of this condition can be Summer Pasture Associated Obstructive Pulmonary Disease or SPAOPD. This is brought on by allergies to pasture allergens and management of this condition is the reverse of the above: horses should be stabled during the day in the summer in well-ventilated and cool areas.