Technical information for veterinarians
Horses with chronic obstructive pulmonary disease (COPD)
Chronic obstructive pulmonary disease-COPD
Chronic obstructive pulmonary disease (COPD) is a lung disease that resembles asthma in humans. The condition is also known as heaves, recurrent airway obstruction, broken wind, emphysema, chronic bronchitis or small airway disease.
Chronic obstructive pulmonary disease (COPD) is common in countries with cold climates, where horses are kept in barns for prolonged periods of time and where hay is often mouldy. Horses that suffer from the condition are usually allergic to mould particles in hay dust, although other allergens such as pollens, chemicals, microbes and substances found in foods, medications and the environment can also trigger the condition.
Chronic obstructive pulmonary disease (COPD) is most often seen in mature horses (usually seven and older) that are stabled during the winter months. It is rarely apparent in warm, dry climates where horses are kept outside all year. Chronic obstructive pulmonary disease (COPD) often causes the premature end to a horse’s athletic career.
The symptoms/diagnosis of COPD in horses
Horses with chronic obstructive pulmonary disease (COPD) will often “heave” to expel air out of the lungs towards the end of exhaling. A wheezing sound at the end of exhalation may also be detected with use of a stethoscope. Coughing, weight loss, lack of energy and intolerance towards exercise are also signs of chronic obstructive pulmonary disease (COPD).
Sometimes, a horse with chronic obstructive pulmonary disease (COPD) may have a mucopurulent nasal discharge (composed of mucus and inflammatory cells), particularly following exercise. The abdominal muscles of horses with chronic obstructive pulmonary disease (COPD) may hypertrophy and form distinctive “heave lines.”
The etiology of COPD in horses
Allergenic micro-organisms in hay, including bacteria, fungi, and minute particles of feed grains, feces, dander, and pollen become aerosols when the horse feeds. Once inhaled, they elicit an allergic response in horses with chronic obstructive pulmonary disease (COPD).
Primary organisms responsible for chronic obstructive pulmonary disease (COPD) are Aspergillus fumigatus, Thermoactinomyces vulgaris, and Faenia rectivirgula.
The fungus A. fumigatus produces spores that are inhaled when they become airborne. These spores are both antigenic and allergenic. The fungi-like bacteria Thermoactinomyces vulgaris and Faenia rectivirgula also produce spores that may be inhaled by the horse.
All breeds are susceptible to chronic obstructive pulmonary disease (COPD) and there may be an inherited tendency towards developing the condition.
Four to six hours after a horse with chronic obstructive pulmonary disease (COPD) is exposed to dust from hay, the airways become acutely inflamed and vast numbers of neutrophils accumulate. These cause the airways to become edematous. Repeated episodes of inflammation can cause the mucosal cells of the airways to proliferate. The combination of this proliferation and edema causes the airway walls to thicken, obstructing normal air flow during breathing.
Mucus is produced in the horse’s trachea and bronchi by the goblet cells of the epithelium and submucosal glands. The viscous, sticky nature of this mucus helps to trap inhaled particles. The epithelium of the trachea and bronchi is covered with cilia which transport the overlying mucous layer up toward the larynx where it is either coughed up or swallowed.
Inflammation of the airways stimulates mucus secretion and causes proliferation of mucus producing cells. The increased mucus helps to transport inhaled allergens out of the airways. When a horse has chronic obstructive pulmonary disease (COPD), the excess mucus within the plugs the bronchioles. The accumulation of mucus and cellular debris in the airways further decreases the diameter of the air passages, which increases the effort required to breathe. The increased effort results in the characteristic abdominal heave displayed by horses with chronic obstructive pulmonary disease (COPD).
Due to the obstruction of air passages, oxygen flow to the alveoli is compromised. This results in the restriction of oxygen to the tissues, impairing the horse’s performance level.
Preventing COPD in horses
With sound management practices, the risk for contracting chronic obstructive pulmonary disease (COPD) can be markedly reduced. The most significant management factors involve the horse’s environment. Dust and moulds will need to be reduced or removed from the horse’s quarters and, if possible, form neighbouring stalls. Other ways to minimize the risk include:
- Turning the horse out as often as possible. (A few horses are allergic to substances in the pasture, so horses should be monitored closely.)
- Reducing dust in the stable by removing bedding such as straw or shavings. Instead, shredded paper or rubber matting should be used.
- Keeping hay away from the horse as much as possible, and ensuring any hay in the vicinity is kept dry.
- Providing a feed that is low in dust such as pellets and alfalfa cubes. Grass silage (haylage) is no longer recommended due to the risk of botulism.
- Removing the horse from the stable when mucking out, to reduce exposure to dust.
- Ensuring that there is good, draught free ventilation through the stable. Half doors and large windows should be kept open at all times. It is better to keep the horse warm by providing more rugs, than by closing off the ventilation.
- Horse owners should be encouraged to maintain their management routine to minimize exposure to allergens. (Few horse owners stick with a plan for the long-term, making recurrence of symptoms likely.)
- Use of lifestyle supplements that help to curb the production of histamines in the tissues can help allergy-prone horses. Bioflavonoids, including those derived from Camellia sinensis and Vitis vinifera, have been reported in numerous studies to inhibit the release of histamines. The antioxidant vitamins A, C, and E can also be helpful for horses suffering from chronic obstructive pulmonary disease (COPD) to help combat free radical damage produced during the stress response and to promote tissue repair.
Treatments for COPD in horses
Lifestyle changes (see above) are the first line of defence against chronic obstructive pulmonary disease (COPD). If these are not effective, or the horse is suffering acutely, you will likely recommend treatment with drugs. These include corticosteroids with anti-inflammatory properties and bronchodilators.
(prednisone, dexamethasone, triamcinolone)
These help decrease smooth muscle contraction and reduce mucus production. They suppress inflammation, providing the horse with fairly quick relief. Corticosteroids can be administered by mouth, by injection, or by inhalation. When administered by mouth or by injection, therapy usually begins with a high dose and, as is reduced to a maintenance level as the horse improves. Inhaled steroids provide a high dose within the airways and minimal systemic side effects but a special mask is necessary for administration.
While corticosteroids are helpful in the short-term, those with potent anti-inflammatory effects are also more likely to cause problems, particularly cardiovascular, immune and wound healing ability problems, when used for long-term therapy. Corticosteroids may be given in oral form or through an inhaler.
(clenbuterol, pirbuterol, albuterol)
These drugs may be safely combined with anti-inflammatory drugs to treat severely affected horses. Bronchodilators may be given orally, by injection, or by inhalation. While oral administration is the most convenient method, inhalation therapy is the most effective treatment for relief of airway obstruction. As with anti-inflammatory therapy, administration of bronchodilators by inhalation requires the use of a special mask.
Equine health options
Recovery®EQ with Nutricol®, is a proprietary lifestyle supplement that can enhance your horse’s quality of life. It may be used on its own or in combination with prescribed medications. See the Oct 2003 review of Recovery®EQ in the prestigious Horse Journal