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Winter respiratory health: Improving a horse’s airway function at work and rest *H&H Plus*


  • The colder months can challenge a horse’s airway function, at work and rest. Richard Hepburn FRCVS offers solutions for the season ahead

    Winter is the perfect time to reassess your horse’s stable management, with the aim of improving the quality of his breathing zone.

    We saw in part one of this series how creating a cleaner indoor living environment, with fewer airborne particles, will reduce the likelihood of airway inflammation and the subsequent development of equine asthma (EA).

    Yet both turnout and exercise can create additional breathing challenges…

    Arena exercise

    The concentration of respirable particles in an indoor arena is dependent upon its setting and construction, both the type and humidity of its surface and the number of horses being trained at the same time.

    Working a horse on a surface liberates particles, which are then dispersed into the school environment. An increased number of horses using the school will worsen this, with trotting and galloping producing the greatest quantity of respirable particles.

    While the effect of different surface types is unclear, the release of particles from damp surfaces is less than that from the same surface when dry. This may be related to surface penetration: when the material is dry, a horse’s feet will sink more deeply and disperse a greater amount of material.

    Further factors will affect arena air quality. If connecting doors to stables are left open during mucking out or forage feeding, this will increase respirable particle levels. Improvements will occur, however, after cleaning the arena border and solid surfaces including seating and obstacles, to remove dust and contamination.

    Ventilation from the outside, away from other sources of dust such as stables, access roads, parking areas and muck heaps, will also help.

    Key message: close connecting doors to stables, but open any windows that will let clean air in, and keep the school surface well-dampened and its surroundings dust-free. A horse with EA should be exercised alone indoors, ideally before others or after a period of ventilation.

    Outdoor work

    Strenuous exercise in cold air has been shown to produce prolonged suppression of local immunity within the lungs, which researchers postulate could increase the risk of respiratory viral infection such as equine influenza. It is unknown if this reduction in immune function has any effect on allergic airway disease, so the traditional advice that a good blast in the cold will help the lungs is unproven.

    Exercising in temperatures below freezing can cause bronchoconstriction, where the airway narrows due to contraction of the surrounding muscle. This can occur any time, from immediately afterwards to several hours later, in otherwise healthy horses. We don’t yet know whether underlying environmental airway inflammation makes this more likely.

    Key message: if your horse has a high breathing rate or is coughing after exercise on a cold day, consult your vet.

    Turnout

    The ultimate improvement in air quality is pasture turnout, which can significantly reverse airway inflammation in severe EA cases. It is important, however, to consider areas where ventilation may not be improved – most importantly, in field shelters and with feeding arrangements.

    Follow the same advice as if the horse was in a stable, ensuring that shelters are airy, clean and free of dusty bedding. If you want to feed dry hay, place it outside on the ground. Similarly, consider whether hard feed in a bucket is a source of respirable particles; if necessary, wet the feed.

    If you need to use round bales, split them open and position them in the windiest spot of the field.

    Key message: consider your horse’s breathing zone, particularly where he can create a small, poorly ventilated area by tunnelling into dry forage. Soaked or steamed hay is a better option for the EA sufferer.

    Grand designs

    Ventilation of buildings is a key factor in airway health. It’s worth considering the movement of air around a horse’s living quarters – not just for the EA sufferer, but with any horse spending more than a few hours indoors.

    Increasing natural ventilation is an effective way of reducing respirable particles, yet the benefit within an individual stable or barn is variable and very localised. Particles must be cleared from the air before the horse inhales them, so any ventilation must be targeted at the horse’s breathing zone – the area at nostril height.

    When building new stables, the air quality in this all-important breathing zone can be considered within the design. For most, however, it’s a case of working with existing buildings and modifying them where possible.

    Mechanical ventilation is aimed at replacing inadequate natural ventilation, so any design or benefit will be specific to a particular stable or barn. Agricultural engineers with experience in calf and dairy cow housing are usually the best people to approach for advice.

    To maximise airflow and enhance air quality in a stable setting, consider:

    1. Bars or grills on the top of stable doors and partitions, or slots between the boards.
    2. No ceiling, with an interior that opens to the roof peak.
    3. Steamed or soaked forage, ideally fed from the floor.
    4. Siting the stable in a windy location, away from outside sources of respirable particles, so that openable windows admit clean air.
    5. “Breathable walls” on the outer barn building, created by leaving gaps within the wall material or using mesh between structural supports.
    6. Low-dust bedding – for all stables in a barn setting.
    7. A sealed, padded floor, to reduce the amount of bedding needed.
    8. An adjoining outdoor area, so the horse can choose to be in or out

    Asthma alert

    Exposure to barn stabling is a risk factor for human asthma. Indeed, the equine and human diseases are thought to be so similar that an understanding of the causative environmental factors can benefit both horses and their owners.

    If your horse’s EA signs persist, despite efforts to improve his air quality, talk to your vet about an appropriate treatment plan. New options include supplementation with docosahexaenoic acid (DHA), which can reduce the time taken for environmental modification to improve airway health, and an equine-specific corticosteroid asthma inhaler – an effective treatment with no systemic side effects. Ask your vet for details

    Ref Horse & Hound; 22 October 2020

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