Plasma cortisol concentration increases within 6 hours of stabling in RAO-affected horses



Reasons for performing study

In many inflammatory diseases plasma cortisol concentration (CORT) increases at the onset of acute inflammation, but the situation in recurrent airway obstruction (RAO) of horses is unknown.

Study design

Split-plot repeated measures design with one grouping factor (disease) and two repeated factors (day and 3-hour intervals).


To test the hypothesis that CORT increases as acute exacerbations of RAO develop.


Four RAO-susceptible and 4 control horses were placed in a low dust environment (LDEnv) for 2 days followed by 2 days in a high dust environment (HDEnv). Exacerbations of RAO were indicated by increases in maximal change in pleural pressure (ΔPplmax) and decreases in breathing frequency variability (BFV), which was continuously measured by respiratory inductance plethysmography. Plasma samples for determination of CORT were collected every 6 h.


In control horses, ΔPplmax and BFV were unaffected by the HDEnv, whereas in RAO-affected horses ΔPplmax increased and BFV decreased significantly. In the LDEnv, there was a circadian variation in CORT in both control and RAO-affected horses. In HDEnv, CORT was unaffected in control horses, but increased significantly in RAO-affected horses between 6 and 12 h after entering the HDEnv.


Plasma cortisol concentration increases concurrently with the development of acute exacerbations of RAO.