The influence of hay steaming on clinical signs and airway immune response in severe asthmatic horses

International audienceBackground: Avoidance of antigenic stimuli was found to significantly reverse airway obstruction of horses withsevere equine asthma (sEA). To date, no published study investigated the influence of steaming hay on lowerairway condition of sEA-affected horses. The objectives were to determine the clinical, cytological and cytokinerespiratory responses of both sEA and control (CTL) horses experimentally exposed to steamed or dry hay.Results: A cohort of 6 sEA horses and 6 CTL horses was involved in this field study. On day 0, both groups werefed with steamed hay for 5 consecutive days, followed by a wash-out period of 26 days prior to be fed with dryhay for 5 consecutive days. Investigations performed 2 days prior to and 5 days after each challenge includedclinical score, tracheal mucus accumulation, and bronchoalveolar lavage fluid (BALF) cytology and cytokine mRNAexpression. Feeding steamed hay significantly decreased its mould content (P < 0.001). Mucus score significantlyincreased when feeding dry hay (P = 0.01). No significant influence of challenge type was found on clinical score.Percentages of neutrophils (P < 0.001) as well as mRNA expression of IL-1β (P = 0.024), IL-6R (P = 0.021), IL-18 (P = 0.009) and IL-23 (P = 0.036) in BALF of sEA affected horses were significantly increased after both (steamed and dryhay) challenges. Relative mRNA expression of IL-1β, IL-6R and IL-23 in BALF were also significantly correlated toneutrophil percentages and both clinical and tracheal mucus score.Conclusions: Steaming significantly decreased mould content but inconsistently influenced the respiratoryresponse of sEA affected horses when fed hay. Based on BALF cytology and cytokine profiles, its relevance mightbe controversial as a non-medicinal therapy for sEA-affected horses