dust, mould, or other airborne particles commonly found in conventional dry hay. Managing the diet is an essential part of treatment, as feed type can influence not only respiratory health but also time budgets and welfare-related behaviours.
Recent research has compared the effects of feeding steamed hay and alfalfa pellets on horses suffering from severe asthma, shedding light on how different low-dust diets affect feeding behaviour, lung health, and overall well-being.
In a controlled study involving nine severely asthmatic horses, Antoine Symoens and colleagues at the University of Montreal, Canada evaluated the effects of two low-dust feeding regimes - alfalfa pellets and steamed hay - on feeding duration, activity patterns, and gastric health.
The horses were housed indoors and first fed dry hay to induce a clinical flare-up of asthma. They were then placed on either steamed hay or alfalfa pellets for four weeks, using a crossover design so that each horse experienced both diets. Their behaviour was recorded for 18–22 hours at multiple stages during the trial, and gastroscopies were performed before and after each feeding period to assess gastric ulcers.
Results showed clear differences in eating patterns between the two diets. When fed steamed hay, horses spent a consistent proportion of their day eating - about 48% - both during the first and fourth weeks of feeding. In contrast, when horses were switched to pellets, the time they spent eating dropped significantly by roughly one-third in the first week. Interestingly, horses on the pelleted diet appeared to adapt by breaking up their feeding into shorter, more frequent meals, a pattern described as “fragmented eating.” This adjustment might help maintain some degree of natural foraging behaviour despite the rapid consumption time associated with pellets.
From a welfare perspective, steamed hay appears to preserve a more natural feeding time budget. Horses in the wild spend most of their day grazing, and maintaining this prolonged eating activity is associated with better digestive health and lower risk of behavioural issues such as boredom or stereotypies. Short feeding times, as seen with pelleted diets, can disrupt this pattern, potentially leading to frustration or undesirable behaviours.
However, feeding choices must also consider respiratory benefits. Earlier findings have shown that while steamed hay is much less dusty than untreated hay, it may be less effective than alfalfa pellets at improving lung function in asthmatic horses. Therefore, while steamed hay supports more natural feeding behaviour, pellets may provide a stronger advantage for respiratory management. Importantly, the study found that neither diet had an influence on the occurrence of squamous gastric ulcers, an encouraging finding for owners concerned about ulcer risk.
In practical terms, managing an asthmatic horse’s diet involves balancing multiple factors. Replacing dusty or mouldy hay with low-dust alternatives, such as haylage, steamed hay, or suitably formulated pellets, can help reduce respiratory irritation. For overweight or laminitis-prone horses, haylage may not be ideal due to its higher energy content, making steamed hay a more moderate choice. Combining different low-dust feeds could offer the best compromise, supporting both lung health and natural feeding behaviour.
In conclusion, when feeding horses with severe asthma, steamed hay helps maintain normal feeding time and behaviour, contributing positively to welfare, whereas pelleted diets offer greater respiratory benefits but may shorten eating duration. Selecting or combining these diets thoughtfully allows owners to meet both the physiological and behavioural needs of asthmatic horses.
For more details, see:
Antoine Symoens, Mathilde Leclère, Valentine André, Marion Desmarchelier,
Behavioral effects of two diets used for the management of severe equine asthma,
Journal of Veterinary Behavior, (2026) Vol 84, pp34-40,
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