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  • Recurrent Airway Obstruction

    Posted on by Abii Dowdy

    RAO, previously termed as chronic obstructive pulmonary disorder (COPD) is a chronic lower respiratory order (meaning it can be found in the lungs and bronchi) seen in horses and ponies. Even though RAO is more common in older horses it can be seen in those as young as 7 years old and it is more likely to affect the stabled horse than the pony who is turned out regularly. RAO is also commonly known as broken wind or heaves.

    FACT: RAO has recently been classified as Equine Asthma Syndrome.

    SPARAO, Summer Pasture Associated Recurrent Airway Obstruction, can affect horses kept outdoors during the summer months. Allergies can be the result of the horse inhaling pollen or outdoor moulds that surface during this season. Even though the clinical signs are very similar to RAO, to be able to manage the condition effectively, stabling is recommended.

    RAO is caused by a hypersensitive allergic response to inhaled airborne dust, most commonly when the horse is stabled or is eating hay. Other pro-inflammatory agents in stable dust include bacterial endotoxins, moulds, forage mites and plant debris.

    RAO is also further exacerbated by high levels of toxic gases in poorly ventilated stables; this includes ammonia from the horse’s urine. There is ongoing research into the condition to try and find further evidence that a genetic predisposition has a part to play in RAO. Currently, several genetic markers have been linked and so it is likely to be a complex process.

    What are the effects of the inhaled particles?

    One of the main effects of RAO is that the diameter of the airways reduces, termed bronchoconstriction, which in turn reduces the airflow and ventilation to the lungs. The cells lining the airway can produce an excessive amount of mucus which sits in the airways and affects the gas exchange in your horse’s lungs. The airway becomes hyper-reactive with the influx of inflammatory cells (mainly neutrophils) and changes in the walls of the airway.

    Clinical signs:

    The clinical signs for RAO and SPARAO tend to vary between different horses and these signs can be reversible if the horse’s environment is managed effectively.

    Important clinical signs to watch out for are: increased expiratory effort, coughing, exercise intolerance, nostril flaring, increased abdominal effort on expiration of breath, nasal discharge and pyrexia (an increased body temperature).

    In severe, acute cases of the disease distressed breathing, flared nostrils, wheezing and obvious abdominal expiratory effort are all apparent at rest. In this case you need to call a vet IMMEDIATELY.

    How do vets diagnose RAO?

    Firstly, they look at the horse’s clinical history before undertaking a physical examination in which they listen to the lung fields with a stethoscope, detecting any abnormal sounds including crackles and wheezes.

    Secondly, the vet can carry out a blood test to rule out possible infectious causes of RAO.

    Thirdly, your vet can undertake an endoscopic examination where a small camera is passed up the nostrils (under light sedation) into the windpipe or trachea. This enables the vet to detect any increased mucus secretion in the trachea and any inflammatory change that may have occurred. A tracheal wash (TW) and bronchoalveolar lavage (BAL) may be performed to retrieve a sample of cells from the trachea and lungs respectively which can then be examined microscopically. An increase in the number of white blood cells, also known as neutrophils, can be suggestive of RAO.

    Lastly, clinical improvement can be seen after a bronchodilator is given.

    This image is of:

    -an endoscope

    -the white blood cells (neutrophils) that you can see in high numbers from a TW or BAL sample under microscopic examination.

    How can RAO be treated?

    One of the most effective treatments for RAO is to reduce the allergens your horse is exposed to. As an owner you can help by feeding your horse haylage or soaked/steamed hay to remove any excess dust particles. Improving the ventilation of your horse’s stable by installing air vents or windows at the back of the stable can also help significantly. Using dust free bedding and ensuring that hay, straw and manure are all stored well away from the stable can make a big difference to the horse affected by RAO. Try to turn the horse out as much as possible and always remove the horse from the box when mucking out. Assess the management of neighbouring stables and, if possible, stable away from stables containing straw or hay.

    Bronchodilator drugs such as Ventipulmin and Dilaterol can be given orally to help alleviate the signs of RAO. However, it is important to note that ongoing regular usage leads to down regulation of receptors and so can become ineffective if used this way. We therefore advise giving pulse treatment, for example, one week on and one week off. Steroids, often used in combination with a bronchodilator, can also be given in feed, injected or inhaled.

    Medication (systemic) vs. Inhaled Therapy

    Systemic therapies are often indicated in severe cases of respiratory distress in horses with RAO and they are easier to administer. However, there tends to be a slightly higher risk of side effects, such as laminitis.

    Inhaled therapies are useful for long-term prevention and are generally well tolerated by the horse. A lower dose of the drug is required to achieve high local concentrations in the affected tissue and so there is a lower risk of side effects.

    Inhaled Therapy inhalers available:

    STEROID ANTI-INFLAMMATORIES: beclomethasone and fluticasone – both these drugs reduce inflammation and mucus production

    BRONCHODILATORS: salbutamol and ipratropium bromide – these drugs relieve the bronchoconstriction and widen the airway. These are used before other drugs to aid their delivery.

    INFLAMMATORY CELL STABILISING AGENTS: sodium cromoglycate – these help prevent RAO.

    All inhalers are used with a spacer device to help optimise the drug delivery to the affected horse, such as an ‘aeromask’, ‘equinehaler’ or ‘aerohippus’.

    Below are some tips on how to use and care for your horse’s inhaler:

    Warm the inhaler to body temperature before use and then shake it for 30 seconds.

    Remove the cap from the inhaler and discard the first spray. Then attach the inhaler to the spacer device ensuring the inhaler itself is vertical.

    Give one spray just before or immediately after the horse begins to breathe in

    If your horse will tolerate it, obstruct both nostrils for 5-10 seconds after breathing in and then allow to breathe normally. This will maximize drug delivery to the correct area.

    Wait at least 30 seconds, shake the inhaler and then spray again.

    Wash the spacer weekly in warm water and washing up liquid before leaving to drip dry.

    Nebulisation therapy is an alternative method of delivering inhaled drugs. This device administers a small droplet of the drug locally, with reduced side effects and a rapid onset of action.

    Things to remember:

    RAO is a chronic condition requiring life-long management. The treatment regime needs to be tailored to the individual horse and environmental management is key. Several medical therapies are available to help alleviate the clinical signs of the condition and aid recovery. Inhalational therapy is useful in disease prevention and control.