Equine Asthma - Veterinary Services

Equine Asthma

Equine asthma, also known as recurrent airway obstruction, is a respiratory disease that restricts the airways of affected horses. ‘Asthma’ is the more modern terminology, which gives a broader definition compared to the previous name of ‘COPD’, (which was known to be a chronic end-point disease). Asthma can be mild, acute or chronic. It is caused by the horse’s immune system reacting to inhaled allergens like mold, pollen, and dust. Equine asthma is progressive, and its symptoms can become severe, leading to airway obstruction, bronchoconstriction, and difficulty breathing.

Some common signs of equine asthma include coughing, increased respiratory rate, audible breathing sounds, nasal discharge, and exercise intolerance. Affected horses may also experience weight loss, fatigue, and reduced performance. Signs can be quite subtle, ranging from a simple lack of energy, to coughing repeatedly, especially when changing pace. Failure to identify early signs of asthma can make it more chronic and difficult to treat in the long-run. Every cough means something and should be investigated!

There are two main types of equine asthma: “summer pasture-associated obstructive pulmonary disease” (SPAOPD) and “recurrent airway obstruction” (RAO). SPAOPD is more prevalent in summer, while RAO is more associated with winter. Here are the reasons why horses can develop asthma in both summer and winter:

1. Summer: Horses with asthma in summer (SPAOPD) are affected by pollen and moulds, especially those found in hay and straw. When horses are out on pasture, they can inhale these pollens, dust, and moulds, leading to inflammation of the airways and subsequent asthma symptoms. In periods of dry weather and lack of rain the risk highly increases.

2. Winter: Horses with asthma in winter (RAO) are affected because they are kept indoors for long periods, often on hay or straw. This can lead to the release of dust and mould spores that horses can inhale, leading to respiratory system inflammation and asthma symptoms.

Both types of asthma are the result of exposure to environmental allergens or irritants, leading to inflammation of the respiratory system. Other factors that can contribute to the development of equine asthma include viral or bacterial infections, stress, and diet.

The diagnosis of equine asthma is based on clinical signs, respiratory examination findings, and laboratory testing. Veterinarians may perform blood tests, bacterial cultures, radiography, tracheal washes or bronchoalveolar lavage to ascertain the presence of the disease.

Treatment of equine asthma commonly includes the use of bronchodilators, corticosteroids, and supportive therapies such as using low-dust bedding and hay, good stable ventilation, and minimal exposure to environmental triggers.

What happens in the lungs?

When a horse has asthma, the lungs undergo several changes that disrupt normal respiratory function. Asthma in horses is characterised by chronic airway inflammation caused by an allergic reaction to inhaled allergens such as spores, dust, and pollens.

In response to the allergen exposure, the horse’s immune system releases cells and chemical mediators that infiltrate the airways and cause inflammation. This inflammation leads to changes in the structure of the airways, causing them to become smaller/constricted, or constricted due to the accumulation of mucus, and less elastic than normal.

Over time, the horse’s breathing becomes laboured, and their airways narrow or obstruct, making it challenging for the horse to breathe normally. In severe cases, respiratory distress results, necessitating medical intervention. The lungs of horses with asthma may also display changes such as thickening of the lining of the airways, damage to airway cells, airway remodelling, and fibrosis, a condition where the lung becomes scarred or rigid.

These changes reduce the horse’s lung capacity, affecting the horse’s physical activity and overall health. Early identification and management of equine asthma is critical to maintain good respiratory health, preserve lung function, and secure a high quality of life for the horse.

Management

Horses with equine asthma require continuous management to avoid exposure to allergens and maintain proper respiratory function. Your vet and vet nurse can help with a management plan that includes monitoring respiratory function, regular weight checks, regular diagnostic testing and tailoring the treatment plan to the horse’s specific requirements.

Even in cases where the environmental management is good, sometimes medical intervention is still needed due to the horse’s own sensitivity level to allergens.

Like human asthma patients, a horse or pony with severe equine asthma has the condition for life. With careful treatment of any flare-ups and making changes to the environment to reduce exposure to allergens, the condition can be managed and horses can enjoy a relatively normal life. However, if the disease goes untreated, there can be long lasting changes to the lung which could impact them in the future and make the condition more difficult to control.

There are resources available for assessing environmental triggers and risks for asthma, so please ask us for more information.

Treatment

There are several different medications available to treat equine asthma, and the choice of medication will depend on the severity of the condition and the horse’s response to treatment. The primary goal of treatment is to reduce airway inflammation and improve lung function. Some common medications used in the management of equine asthma include:

1. Bronchodilators: These medications work by relaxing the smooth muscles in the airways, allowing air to move more freely in and out of the lungs. Common bronchodilators used in equine asthma include albuterol and clenbuterol (aka Ventipulmin). Although they work by opening the airways allowing the horse to breathe more easily, they do not treat the inflammation which is causing the airways to narrow. Often it is necessary to prescribe steroids to manage things longer term, as the condition can take a while to settle (and flare up again regularly).

2. Corticosteroids: These medications help to reduce airway inflammation and swelling. Corticosteroids commonly used in horses include fluticasone, dexamethasone, and prednisolone.

3. Antihistamines: These medications may also be used in the management of equine asthma to block the effects of histamines, which can cause airway inflammation.

4. Anti-inflammatory drugs: These medications help to reduce inflammation in the lungs and airways. Common anti-inflammatory drugs used in equine asthma include NSAIDs like phenylbutazone and firocoxib.

5. Immunotherapy: In some cases, immunotherapy may be recommended, which involves exposing the horse to small amounts of the allergen over time to desensitise them. This type of therapy is typically used in cases of severe or chronic asthma.

It’s important to note that the use of medications in the management of equine asthma should be under the guidance of a veterinarian. Proper management of asthma in horses, including environmental management and lifestyle changes, plays a crucial role in improving the prognosis of affected horses, and helps to prevent the recurrence of clinical symptoms.

Delivery methods

The best delivery method for equine asthma medications depends on the severity of the condition, the nature of the medication, and the horse’s individual response. Here are the most common delivery methods used for equine asthma medications:

1. Inhalers: Inhalers are one of the fastest and most direct methods for delivering medication to the lungs, where it is required. Inhalers for horses typically include a pressurised canister of medication that is administered through a mask placed over the horse’s nose. These are often used in treating acute symptoms of equine asthma.

2. Nebulisers: Nebulisers are commonly used to deliver medication to horses with more severe respiratory conditions, including asthma. The device converts liquid medication into a mist that the horse inhales through a mask over its nose. Nebulisers are effective in treating both acute and long-term asthma symptoms.

3. Oral medications: Some medications, such as corticosteroids, can be given orally in the form of pills, syrups, or injectables. However, oral medications are not always considered as effective as inhaled medications. Additionally, the medication may take longer to work if given orally.

4. Intravenous medications: Intravenous medications give more severe cases of asthma or allergic reactions, often administered in an emergency situation.

It’s important for horse owners to follow their veterinarian’s instructions on medication dosage, frequency, and duration to ensure optimal health outcomes for their horses.

Difference between asthma and infection?

An upper airway infection in horses is a respiratory illness caused by a viral or bacterial pathogen that affects the horse’s nasal cavity, throat, trachea, and lungs. This illness can produce mild or severe clinical signs, depending on the infectious agent and the horse’s overall health status.

The symptoms of an upper airway infection typically present as a combination of coughing, nasal discharge, fever, lethargy or dullness, and loss of appetite. Horses may also exhibit laboured breathing, decreased performance, and difficulty swallowing. The severity of infection and the specific pathogens involved may vary from case to case.

Viruses are the most common cause of upper airway infections in horses. They are highly contagious and can spread quickly among horses sharing the same environment. The most common viral pathogens linked to upper respiratory infections in horses include equine herpesvirus (EHV) and equine influenza virus (EIV).

Bacterial infections, such as Streptococcus equi (Strangles), can also cause upper airway infections. Bacterial infections are less common than viral infections and may persist for a more extended period than viral infections.

In many cases it is necessary to perform an endoscopic examination to allow collection of bronchiolar or tracheal fluid to distinguish between asthma and other respiratory conditions, such as chronic infection.

Treatment of upper respiratory infections in horses typically includes supportive care, such as rest and hydration, and symptomatic treatment using non-steroidal anti-inflammatory drugs (NSAIDs) to alleviate fever and decrease inflammation. Specific antibiotics prescribed by a vet may be used in cases of bacterial infections.

To reduce the risk of infection, many preventive measures such as minimising stress and isolation of new animals to monitor for upper airway symptoms in introduced animals, vaccination regimes and vaccination boosters, proper quarantine measures, and stringent biosecurity practices should be put into place.

It is important to note that equine asthma is non-infectious, whereas upper airway infections can be spread from horse to horse! However, infection can occur alongside and secondary to asthma.

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