Differences in pulmonary functional indices derived from the single-breath diagram for CO2 (SBD-CO2) in horses related to age, sex and usage.

Although pulmonary function tests have been used to evaluate horses with clinically normal lungs and those with recurrent airway obstruction (RAO), comprehensive studies of equine respiratory function, considering factors such as sex, age and usage are not available. Studies on the influence of these factors on pulmonary function in healthy horses are required for interpretation of measurements made in those with respiratory disease. The study was performed with 63 warmblood horses and the status of their pulmonary health was evaluated by clinical examination. The functional aspect of pulmonary health was assessed by indices derived from the single-breath diagram for CO2 (SBD-CO2). Differences in pulmonary functional indices between the sexes, age groups and usage groups adjusted for pulmonary health were analysed with hierarchical linear models. It was shown that the effects on pulmonary function of age, sex and usage of a horse were significant and have to be considered when establishing the true pulmonary functional status of a horse suffering from RAO. The multivariate statistical model used included the covariates age, sex and sporting discipline of the horses and accounted for the complex, non-linear interactions between the different covariates.