For most horses, winter means more time confined to the stall or indoor arena. Unfortunately, protection from the weather can come at the expense of lung health for some equines.
Inflammatory airway disease
Inflammatory airway disease (IAD) is a condition characterized by few symptoms except a cough when the horse is at rest. When exercising, however, it shows up as poor performance, exercise intolerance, or coughing, together with an inflammatory reaction in the lung, often with excess mucus. This is unrelated to infection.
IAD can occur at any age, but the first bout is typically triggered by stall confinement and exposure to common irritants such as dust and molds from straw and hay, and airborne bacterial endotoxins, as well as ammonia.
Recurrent airway obstruction (RAO), is a chronic allergic and/or hypersensitivity reaction that may have some similarities to the human condition “farmer’s lung”. Airflow is obstructed by a combination of inflammation, mucus and bronchospasm. In the later stages, gas exchange may be compromised because of irreversible damage to the lung tissue.
A major difference between IAD and RAO is the symptoms that present at rest with the latter. These include coughing, flared nostrils, expiratory wheezing, and a prominent “heave line” at the junction of the chest and abdomen where the diaphragm muscle is located. Ability to exercise is severely compromised, although correct management and treatment can ease or eliminate symptoms as long as there is yet no permanent damage.
Prevention and management
In both conditions, exposure to high concentrations of organic and inorganic material in the air can both cause and worsen symptoms. The last place these horses should be is inside a tightly closed barn. If the horse must be confined, you should guarantee good circulation of fresh air throughout the barn. Bedding should consist of woodchips or paper in all the stalls, not just those of affected horses. Hay should not be stored in the same building and should be wetted down thoroughly before feeding.
Many effective systemic and inhaled drugs can be tried and this approach should be discussed with your veterinarian. Some horses can be managed with reduced or no drugs, through a combination of environmental management and supplements.
Supplementing for lung health
Several studies have identified oxidative stress as a component of lung disease in the horse. A 2012 study found reduced serum levels of the antioxidants copper, zinc and selenium, and the glutathione enzyme system. A 2006 study found significant decreases in vitamin C in the lung fluid of RAO horses exposed to organic dusts (mold); vitamin C has been shown to be a major antioxidant in the equine lung. Revving up the glutathione system in the lungs can also help protect against the effects of organic acid exposure.
Horses can synthesize their own vitamin C and those on fresh pasture also have very generous amounts in their diet. For horses not on green pasture, supplementing 1000 to 4000 mg/day is reasonable to help counteract the drops caused by lung disease.
Plant-based antioxidants both directly combat oxidative stress and also have a sparing effect on vitamin C and the glutathione enzyme system. These antioxidants include citrus bioflavonoids, quercetin, grape seed extract, N-acetyl-cysteine and herbs such as turmeric.
Spirulina is also an antioxidant with the added benefit of blocking histamine release, and is often very helpful for horses with lung disease at a dose of 2 grams/100 lbs bodyweight, given twice daily. Bronchospasm can be directly addressed by the use of Gynostemma pentaphyllum (Jiaogulan) at 20 mg/100 lbs bodyweight.
If you suspect breathing issues, get a diagnosis as soon as possible. Management changes and supplementation can be very effective in mild and moderate cases, and may reduce the need for medications at all stages.