Do environmental factors influence hair cortisol in foaling season?

Plasma cortisol (C) in adult horse is influenced by several environmental factors, such as temperature and lighting conditions but to date it is not clear if also hair cortisol is subjected to the same factors. The aim of this study was to investigate the influence of these environmental factors on foal hair cortisol levels at 30 days of age during the breeding season. Hair samples were collected from 69 foals at 30 days of age from March to July and analyzed for C by RIA. For each sample were considered the averages of environmental factors (lighting conditions and temperature) during the 30 days preceding the sampling. Hair cortisol levels were 37.32±8.87 pg/mg (mean value ±SD). None of the climate variables was related to cortisol hair concentrations. In conclusion these data suggest that hair cortisol in 30 days old foals is not affected by the influence of temperature and lighting conditions and cortisol variations are due to an individual HPA axis activation and not to environmental factors.