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Equine Asthma

Equine asthma is the term used to describe inflammatory disease of the horse’s airways. The term “asthma” has been introduced recently since the horse’s condition is similar to that in humans: asthma in both species involved chronic airway inflammation and limitation of expiratory airflow, and both have gradations of severity. The underlying causes of equine asthma are not well-understood, but airway hyperresponsiveness to dust, mold, and other environmental particles seems to occur.    

There are two subgroups of equine asthma that are generally based on severity. Inflammatory airway disease (IAD) is a mild condition seen in horses of any age that may present with mild coughing and nasal discharge. Horses with IAD tend to breathe normally at rest and have minimal changes in lung function. This condition is more common in stabled horses. The signs of IAD may improve spontaneously or with treatment, and the signs often do not recur. There is a subset of IAD that is seen in young racehorses in training.

Recurrent airway obstruction (RAO) is a severe condition mostly seen in horses more than seven years of age. Horses with RAO have increased respiratory effort at rest, exercise intolerance, often severe coughing, and possibly nasal discharge as well. RAO may worsen seasonally, and it can be found in both stabled and pastured horses. Horses with IAD (mild asthma) do not necessarily progress to having RAO (severe asthma). RAO can improve with environmental modification and medical treatment.

DIAGNOSIS:

Diagnosis of equine asthma starts with a physical exam by your veterinarian. In addition to checking vital signs, your vet will listen carefully to your horse’s lungs at rest and after exercise or a “rebreathing exam.” A rebreathing exam asks the horse to breathe into a bag for a short time period to stimulate them to take deeper breaths—this improves our ability to hear subtle changes in lung sounds. Blood testing may help to differentiate equine asthma from infectious respiratory disease, which can present with many of the same clinical signs but which is treated very differently. Horses with severe asthma are more prone to developing pneumonia (lung infection), so this step is especially important. Other diagnostics available include upper airway endoscopy, which allows your vet to look at the upper airways, the trachea, and the openings to the lower airways. Horses with asthma often have excessive mucus in their airways. While performing endoscopy, we can instill a small amount of saline into the airways and then collect a sample of it to examine the types of cells found in the horse’s airway secretions. This may help differentiate among different respiratory conditions and to help measure severity (e.g. IAD vs RAO). If pneumonia or severe changes to the lungs are suspected, ultrasound and x-rays of the chest may also be performed for more information.

TREATMENT:

Treatment requires environmental modification to decrease the triggers of airway inflammation. The degree of environmental modification recommended to improve clinical signs often depends on their severity. For example, a horse having an episode of IAD/mild asthma may improve if you:

- immerse its hay in water to reduce dust prior to feeding

-feed hay on the ground to reduce dust in “breathing zone”

- improve ventilation in the barn

- use low-dust bedding

-use a hay steamer to reduce dust in the hay

A horse with RAO/severe asthma may need

-full time pasture turnout (as long as RAO is not pasture-associated)

-switch from feeding long-stem hay to steamed chopped hay, hay extender, or complete pelleted feed

Please see information at the end of this document for examples of products used in environmental modification. Remember to make any diet changes gradually over 1 to 2 weeks to allow the horse’s intestinal microbes to adjust.

Horses with asthma often are given medications to help relieve respiratory distress while environmental modification is being instituted. It is important to remember that with severe asthma, signs are very likely to recur once medication is discontinued if there has been no change in the environment.

Since asthma is an inflammatory problem, the most effective medications are corticosteroids, which have potent anti-inflammatory and immunomodulatory effects. Dexamethasone is a very potent corticosteroid that can be given as an injection or as an oral medication. Prednisolone is a less potent corticosteroid that is given orally. Your veterinarian will give you specific instructions for using these medications since many require a tapered course to allow the body to readjust to producing its own corticosteroids as the medications are discontinued. Although they are highly effective, corticosteroids have many potential adverse effects, including increased susceptibility to infections, increased drinking and urination, and possibly a higher risk of laminitis.  Your vet may recommend testing for PPID (aka Cushing’s Disease) in older horses with asthma; the bodies of horses with PPID already make excessive corticosteroids and adding one of these medications may increase the risk of adverse effects.

Other common medications used for asthma are bronchodilators such as clenbuterol. These medications do not treat the underlying inflammation of asthma but may help relieve coughing. They relax the muscles in the small airways and improve clearance of mucus. It is important to decrease dust in the environment when giving these medications to avoid exposing smaller airways to more particulate matter as they are dilated. Clenbuterol is probably effective for longer if it is used along with a corticosteroid due to the pharmacologic interactions of these medications. Adverse effects may occur but are less worrisome than those of corticosteroids.

Corticosteroids, bronchodilators, and other medications may be administered directly to the airways via inhaler or nebulizer (see below). Theoretically this should result in fewer body-wide adverse effects.

Lastly, there is some promising research about the role of an omega-3 fatty acid supplement in horses with asthma (see below). One product showed some benefit in horses with asthma when combined with a low dust (no hay, complete pelleted feed) diet compared with a low dust (no hay, complete pelleted feed) diet alone. It's possible that the supplement could have some effect in horses that are continuing to eat regular hay or steamed hay, but there is no research to support that.

ENVIRONMENTAL MODIFICATION OPTIONS:

1) Make-your-own hay steamer:

Many clients choose to make their own hay steamers out of utility trunks and piping. If you are interested, I can forward you an email from one of my former clients in which she explains her hay steamer construction and setup, including photos. Apparently there are some helpful videos on youtube that got her started.

2) Commercially-available hay steamers:

a) Haygain hay steamers:

https://www.haygain.us/

b) Hay Medic USA/Happy Horse Hay Steamer: less expensive than Haygain but expensive shipping fee from Canada:

http://www.happyhorseproducts.ca/index.asp?mid=5&mid2=195

3) Inhalers:

Here is an example of an equine inhaler:

https://www.trudellmed.com/animal-health/aerohippus

4) Nebulizers:

Here is an example of an equine nebulizer:

https://www.flexineb.us/

5) Hay substitutes: examples of chopped/bagged, cubed, pelleted forage products. Consider feeding a ration balancer or vitamin/mineral supplement if you are not feeding a complete pelleted feed.

a) Triple Crown Safe Starch: not steamed but still less dusty than regular hay.

https://www.triplecrownfeed.com/products/safe-starch-forage/

b) Triple Crown Timothy Balance Cubes: steamed and thus less dusty. MUST BE SOAKED BEFORE FEEDING TO AVOID CHOKE (ESOPHAGEAL OBSTRUCTION).

https://www.triplecrownfeed.com/products/timothy-balance-cubes/

c) Hay pellets—may be alfalfa or grass hay, may or may not contain molasses. Here is an example of a Timothy hay pellet:

Poulin Pellet Mini Bites or Poulin Pellet Super Bites

We also recommend SOAKING hay pellets prior to feeding to avoid choke.

d) Complete feeds: these provide all the forage a horse needs as well as needed vitamins and minerals.

Examples of complete feeds: Purina Equine Adult, Purina Equine Senior, Triple Crown Senior, Nutrena SafeChoice Senior.

6) Potentially helpful omega-3 fatty acid supplement:

Aleira (made by Arenus):  http://arenus.com/aleira

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