Hair cortisol level as a retrospective marker of hypothalamic–pituitary–adrenal axis activity in horse foals

Stimulation of the hypothalamic–pituitary–adrenal (HPA) axis and elevated cortisol concentrations in fetal plasma are associated with foal maturity, viability and adaptation to independent life. However, non-invasive measurement of cortisol in hair samples has not yet been validated in horses. The current study developed a radioimmunoassay to analyse cortisol in horse hair and was used to measure cortisol hair concentration at birth and at 30 and 60 days of age as a retrospective study of HPA axis activity. Cortisol was detectable in the hair of foals from birth until 2 months, but decreased with time and varied greatly between individuals. Analysis of hair cortisol could be useful for non-invasive retrospective studies of HPA axis activity in perinatal horse.