SCIENCE SUPPLEMENTS Respiratory Disease: Part 4. Treatment and prevention of common equine respiratory diseases

Dr Kirstie Pickles

Last week we looked at diagnosis of some of the more common causes of respiratory disease in horses SEE HERE  This week we will discuss how these respiratory conditions can be treated and prevented.

Treatment of Equine Respiratory Disease

Treatments commonly used in equine respiratory disease include:

  • Antibiotics: when there is evidence of bacterial infection, e.g. pneumonia, these may be given orally, by injection, or occasionally by inhalation. Due to growing antimicrobial resistance, antibiotics are usually now only prescribed if there is clear evidence of bacterial involvement (e.g. culture of respiratory secretions such as tracheal wash).
  • Bronchodilators: drugs which open up the airways (e.g. Ventipulmin®) to allow the horse to breathe easier and to aid mucus clearance. These may be given in feed, intravenously or by inhalation. The horse’s airway very quickly develops tolerance to Ventipulmin® (after 2-3 weeks) and therefore this drug is best used as ‘rescue therapy’ for short-term treatment of disease exacerbations. Other bronchodilators to which the horse does not develop tolerance are available for use by inhalation only (e.g. Atrovent®).
  • Anti-inflammatories (steroids): drugs that reduce inflammation (e.g. dexamethasone) are the mainstay of allergic inflammatory conditions such as equine asthma. These may be given intravenously initially with maintenance daily doses in feed or, ideally, by inhalation (Fig. 1). In general, inhaled steroids are preferred due to more targeted delivery
    Fig. 1: Horse with equine asthma receiving steroids by inhalation.

    and reduced uptake of drug into the body, thereby reducing unwanted side effects.

  • Non-steroidal Anti-inflammatories: drugs such as phenylbutazone (‘bute’) may aid decrease fever in infectious diseases such as pneumonia but are of no benefit in equine asthma.
  • Antioxidants: High dose antioxidant supplements have been shown in several controlled studies to be beneficial in reducing clinical signs of respiratory disease.
  • Environmental Hygiene: a low dust environment is critical in helping resolve asthma and will be beneficial in any lower respiratory tract disease (see below).

Preventing / Reducing Risk of Equine Respiratory Disease

Good Environmental Hygiene

Many studies have shown that a major contributing factor in equine respiratory disease is the poor air quality in the stable. The main factors that relate to air quality in the stable are the quality of bedding and forage, the flooring and the ventilation. Several studies have shown that people working with horses in stables for 6-8h each day have increased respiratory symptoms compared with those who don’t work in stables. Clearly, if a horse is breathing the same air for 3-4 times longer each day, the effect on their respiratory health will be even greater.

Flooring: The ideal flooring is a sealed rubber floor with a built-in slope towards a drain or the stable door that is easy to clean with a pressure washer or hose and brush. A sealed rubber floor allows the amount of bedding in the stable to be reduced which in turn reduces the amount of dust in the stable. Rubber floors can be sterilised reducing the number of bacteria on the floor therefore decreasing the production of ammonia. As a guide, if you can smell ammonia in a stable then it is already at a level that will cause irritation of the horse’s airways.

Forage: The ideal forage will have a low level of respirable dust (dust of a size that can be breathed into the small airways of the lungs). Haylage or steamed hay are best as they contain minimal dust and mould spores. Soaking hay has been shown to reduce respirable dust by 60-70%. Full immersion in a bucket and immediate feeding is as effective as soaking for up to 12 hours. If using prolonged soaking, tubs need regular cleaning to remain hygienic and therefore immersion is probably preferable to soaking. Soaking also reduces the nutritional value of the hay as water soluble vitamins, minerals and carbohydrates (sugars) are lost into the water. This can be an advantage in managing some horses (e.g. laminitics). Steaming hay reduces dust and kills mould spores without removing nutritional value. Not all steamers perform as well, but good commercial units significantly improve the hygienic quality of hay, are quick and simple to use and result in less loss of nutrients.

Bedding: The ideal bedding is dust free, absorbent, inexpensive and will encourage the horse to lie down. In the past 25 years in professional racing and sport horse yards, large-chip shavings have essentially replaced straw as the first-choice bedding. However, recent studies showed that horses actually lay-down more on straw than on shavings. Good straw may in some cases contain less fungi and bacterial toxins than ordinary low-quality shavings. Paper or cardboard (Fig. 2) are also excellent, low dust bedding options.

Fig. 2: Cardboard is an excellent low dust bedding

Ventilation: Many traditional stables have poor ventilation and this can be made worse when owners shut windows and stable top-doors during poor weather. Adequate ventilation requires two openings for airflow, e.g. the top stable door being open and an open vent in the back wall. Horses with rugs on are perfectly able to cope with draughty, well-ventilated stables. The dislike and concern over draughts is a human problem, not a horse one. Closing the stable top-door and window for even a single night may be enough to cause a flare-up in more susceptible horses.

Management Practices

Mucking Out: Remove your horse from the stable whilst you muck-out as this generates a tremendous amount of respirable dust which will remain in the air for at least 30 minutes. Try to make sure all windows and doors are open when you muck-out and wait at least 30 minutes before putting your horse back in the stable.

Feeding: Feeding forage and hard-feed (wetted) from the floor will encourage head lowering. This allows any respiratory secretions to drain out of the windpipe and nose. Not only will this allow you to become aware of any secretions, it also avoids pooling of the secretion in the lower windpipe which increases the risk of secondary bacterial infection.

Turnout: Generally, time out of the stable is extremely beneficial in reducing respiratory disease, especially if horses can perform natural grazing behaviour. The one exception to this is horses that suffer from summer associated equine asthma due to allergies to tree, flower, crop and/or grass pollens. Such horses may need to be stabled in the summer to avoid disease exacerbations.

For horses prone to obesity and laminitis, rather than shorten or avoid grazing, the use of grazing muzzles should be considered. These restrict the amount of grass the horse can actually eat but at the same time the horse is out of the stable (which reduces exposure to stable dust) and has its head lowered (which aids clearance of material from the airways). Even turnout in bare paddocks with hay/haylage fed from the floor is beneficial to maintain respiratory health compared with stabling.

Vaccination: Keep your horse up to date with relevant vaccinations. Vaccination may or may not prevent your horse from infectious disease. However, in most cases, if a vaccinated horse does contract an infection, the severity and duration are usually reduced compared with unvaccinated horses.

Travelling: Travelling can induce respiratory disease or worsen symptoms in horses with existing problems such as asthma. Travel with good ventilation and make sure forage is soaked or feed steamed hay or haylage and use a low dust bedding.

Fig 3: Horse with pleuropneumonia (infection of lungs and chest cavity) with a chest drain to allow drainage of purulent fluid from the chest cavity.

Check appropriate feed and bedding is available at the venue if you are staying away at competition; if not, take your own.
Always check your horse’s temperature before travelling. If your horse has a temperature, then it is unwise to travel and compete as the risk of respiratory disease will be increased. Long travel (over 6h) is a known risk factor for pleuropneumonia, a serious bacterial infection of the lungs and chest cavity (Fig. 3). The longer the journey, the more important it is to think about respiratory disease. Long journeys should be broken up to allow rest periods for the horse where it can lower its head to the ground.

Scoping: Because horses can often have mild-moderate respiratory disease and not show any signs, if you are competing it is advisable to ask your vet to ‘scope’ your horse at the start of the season, mid-way through the season, at least 2-3 weeks before any major competitions, and for any event where you might have to travel more than 6 hours. The reason for ‘scoping’ 2-3 weeks in advance is to allow time for laboratory analysis of samples your vet may take from the airways, time for treatment, and time for withdrawal of medication before competition.

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