Objective - To evaluate the phospholipid composition and function of surfactant in horses with recurrent airway obstruction (RAO) at various clinical stages and compare these properties with findings in horses without RAO. Animals - 7 horses with confirmed RAO and 7 without RAO (non-RAO horses). Procedures - Pairs of RAO-affected and non-RAO horses were evaluated before, during, and after exposure to hay. Evaluations included clinical scoring, lung function testing, airway endoscopy, and bronchoalveolar lavage fluid (BALF) absolute and differential cell counts. Cell-free BALF was separated into crude surfactant pellet and supernatant by ultracentrifu-gation, and phospholipid and protein concentrations were determined. Phospholipid com-position of crude surfactant pellets and surface tension were evaluated with high-perfor-mance liquid chromatography and a pulsating bubble surfactometer, respectively. Findings were compared statistically via mixed-effects, repeated-measures ANOVA. Results - Total phospholipid concentration in BALF was lower in RAO-affected versus non-RAO horses at all sample collection times. In the RAO-affected group, total phospholipid concentration was lower during exposure to hay than before or after exposure. There were no significant differences in BALF protein concentration, percentages of phospholipid classes, or surface tension between or within groups of horses. Conclusions and Clinical Relevance - All clinical stages of RAO-affected horses were characterized by low surfactant concentration in BALF. Exacerbation of RAO led to an additional decrease in surfactant concentration. Causes for low surfactant concentration in RAO-affected horses remain to be determined. Low phospholipid concentration may render RAO-affected horses more susceptible than unaffected horses to surfactant alterations and contribute to clinical disease status and progression.
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