Even mild equine asthma impairs oxygen uptake in the lungs and decreases athletic performance and in older horses and horses not in work can lead to loss of condition. Horses with asthma are frequently treated with steroids (e.g. Equisolon, Clenil) and bronchodilators (e.g. Ventipulmin, Ventolin). Although these drugs reduce airway hyperreactivity and hypersensitivity, the level of inflammation in the lungs (shown by lung wash cell counts) usually does not decrease, even after months of therapy, if air quality is not improved. Treatment with bronchodilators should always be used in conjunction with reduced exposure to dust to ensure that the amount of particulates reaching the lower airways is not actually increased. A recent study published by a group of researchers at the University of Calgary in Canada (Bond et al. (2020) investigated the effect of common asthma drugs and improved environmental airway hygiene on aerobic performance of asthmatic horses.
The study involved 12 fit, Thoroughbred polo horses with mild asthma following exposure to poor air quality due to bushfire smoke over a month. The horses had a history of coughing and decreased performance during the period of exposure to smoke. Air quality improved at the start of the trial with number of particulates capable of reaching the lower lungs decreasing from 36 to 7 ug/m3. A lung wash and exercise testing were performed and the horses were then randomly allocated to receive either steroid (6 horses) or saline (6 horses) by intramuscular injections once a day for 20 days. The person administering the treatments and performing the respiratory and statistical analysis was blinded to the treatment groups. Performance testing was repeated on day 16 and then again on day 17 after use of an inhaled bronchodilator. Lung wash repeated on day 20.
The authors found that the single most important factor in improving aerobic capacity in these horses with mild asthma appeared to be improved environmental conditions as documented by significantly decreased air particulate counts (i.e. there was no difference between the saline group and the group administered steroid). Aerobic capacity significantly increased as particulate concentrations decreased. The addition of an inhaled bronchodilator prior to performance testing did not affect aerobic capacity, regardless of whether horses had received steroid administration. Lung wash cell populations (i.e. lung inflammation) were also not decreased by steroid treatment.
The authors concluded that “This study highlights the importance of improved air quality on functionally significant airway inflammation.” Although this study investigated horses with mild asthma due to smoke inhalation, it is reasonable to assume that the findings would equally apply to horses with the naturally occurring form of equine asthma from allergens and particulates in the stable and/or field environment.
Horse stables can have very high particulate counts from inorganic dusts and organic mould spores, mite debris, microbes and vegetative matter. Additionally, irritant gases like ammonia can reach high concentrations, particularly in deep litter systems. This poor air quality will also affect your lungs – an additional reason to improve it! If you have a horse with asthma, ways you can improve the air quality include:
• Increasing pasture turnout; ideally 24/7 as particulate counts outdoors are far lower than in a stable
• Provide 2 air openings in stables e.g. top half of stable door and an open window frame. If it’s cold add rugs rather than close up the doors and windows
• Replace dry hay with haylage or steamed hay. Soaking hay will decrease particulates but is far inferior to haylage or steamed hay
• Replace straw with dust-free options like paper or dust-extracted shavings and avoid deep litter systems
• Consider a switch to rubber matting. This allows much less bedding to be used, makes mucking out quicker and saves both time and money in the long run
• Remove horses from stables whilst mucking out
• Keep hay/straw stores and muck heaps well away from horses.
On yards, it is often not possible to fully optimise the stable environment. Additionally, horses with asthma caused by environmental allergens, such as tree pollens, also struggle when maintained outdoors. Feeding a supplement containing high levels of bioavailable antioxidants and essential fatty acids can be useful in optimising airway health.
Bond, SL, Greco‐Otto, P, MacLeod, J, Galezowski, A, Bayly, W, Léguillette, R. Efficacy of dexamethasone, salbutamol, and reduced respirable particulate concentration on aerobic capacity in horses with smoke‐induced mild asthma. J Vet Intern Med. 2020; 1– 7.
To view study click HERE