Originally published on EquiMed.com
Chronic respiratory disease is common in horses. The best known condition is chronic obstructive pulmonary disease (COPD), a disease characterized by chronic cough, increased respiratory rate, forced abdominal breathing, and exercise intolerance.
If your horse must be stabled, removing dry hay from the diet is the most important aspect of environmental control, and, in mild cases, soaking the hay prior to feeding is often effective in reducing dust levels in the horse's breathing zone.
Feeding and housing management play a critical role in the perpetuation of COPD. Specifically, dusts and molds contained within feed and bedding can trigger the allergic responses within the lungs that ultimately result in development of COPD. Therefore, management of affected horses is heavily reliant on measures that minimize exposure to these airborne irritants.
“My horse has allergy problems” is not an uncommon statement by horse owners. Nutritionists are frequently put on the defensive by this statement because, in many situations, diet is identified as the most likely cause for these problems.
Allergy or, more correctly, hypersensitivity refers to an altered state of immunoreactivity resulting in self-injury. Stated another way, an allergic reaction occurs when the immune system “overreacts” to a specific stimulus. Clinical signs of hypersensitivity reactions will vary depending on the severity of the reaction, the body system(s) involved, and whether the reaction is localized or generalized.
In the horse, the skin and the respiratory tract are frequently affected by hypersensitivity reactions. Urticaria, contact dermatitis, and insect hypersensitivity are examples of hypersensitivity-induced skin disease.
Some authors and, in particular, commercial laboratories that offer allergy testing services believe that food allergy (to feed ingredients such as oats, corn, alfalfa, beet pulp, and barley) is an important cause of these skin reactions.
The infamous “protein bumps” is an example of an urticarial reaction. In reality, skin hypersensitivity reactions are very rarely due to diet. More commonly, these reactions are due to insects, parasites, bedding, tack, drugs, and various other agents that, upon contact with the skin, may trigger a hypersensitivity reaction.
The main cause of COPD is an allergic response to organic dusts, including molds in feed and bedding. In this respect, equine “heaves” resembles those human occupational lung diseases caused by inhaled organic dusts.
Research shows that dust in horse stables contains over 50 types of molds, large numbers of forage mites, endotoxins, and other inorganic factors. The primary source of organic dust is hay and straw. Many of the molds contained in hay and straw are sufficiently small to reach and deposit in the small airways of the lungs when breathed in by the horse.
Although horses can and do inhale organic dusts present in straw, hay is the major source of these aeroallergens. Characteristic feeding behavior, such as eating hay for long periods and shaking the hay, results in dust concentrations in the breathing zone that are much higher than in the rest of the stable.
Therefore, while bedding and barn ventilation are considerations in improving the environment of COPD-affected horses, it is more important to remove the offending hay.
If the horse must be stabled, removing dry hay from the diet is the most important aspect of environmental control. In mild cases, soaking the hay prior to feeding is often effective in reducing dust levels in the horse’s breathing zone.
The hay must be thoroughly soaked, preferably by immersing the hay in a large tub of water for a 10-15 minute period. Dry areas in a poorly soaked hay portion can release enough mold spores to cause an allergic reaction. This process should be done no sooner than 20 to 30 minutes before feeding to avoid leaching of water-soluble nutrients from the hay.
A much less labor intensive approach involves use of alternative forages such as hay cubes, haylage, or complete pelleted feeds. Clinical experience has shown that these hay alternatives are necessary in severely affected horses. Haylage and silage are becoming more popular in the industry.
Owners are advised not to use broken or damaged haylage/silage bags and to use open bags within two to three days of opening; mold counts in haylage or silage can increase rapidly after exposure to air.