Is it getting in the hair? - Cortisol concentrations in native, regrown and segmented hairs of cattle and pigs after repeated ACTH administrations.

Adrenocorticotropic hormone (ACTH) is part of the hypothalamic-pituitary-adrenal axis response to stress and induces the release of cortisol, which is commonly used as an indicator in stress and animal welfare research. In recent years, hair cortisol concentration (HCC) gained increasing importance as a promising retrospective indicator for stress in animals. Thus, the aim of our study was to validate HCC as a potential indicator of increased endogenous cortisol release in cattle and pigs by repeated ACTH administrations followed by cortisol analysis in different hair types. For this purpose, 34 cattle and 38 gilts were treated either with repeated i.m. injections of ACTH or saline every second day over a period of 4 weeks. Saliva samples were taken before and after injections once a week from selected animals to verify the endogenous cortisol response. At the end of the treatment (week 4) and after 8 and 12 weeks, samples of natural and regrown hair were taken from the caudo-dorsal region of the back and analyzed for cortisol concentrations. In addition, natural hair was sampled after 12 weeks and cut into segments prior to analysis. Treatment with ACTH revealed a significant increase in salivary cortisol after application in both species, although this increase was attenuated in pigs compared to cattle. In week 4, HCCs were significantly elevated in natural and regrown hair of ACTH-treated animals. In cattle, HCCs significantly increased after ACTH treatment in natural, regrown and segmental hair compared with control animals, indicating that HCC may be a promising indicator of stress, as cortisol levels in all hair types reflected the preceding period with increased cortisol release. In pigs, there were no differences in HCCs between treatments. This may be caused by the lower systemic cortisol response in pigs, but seasonally reduced hair growth and external cross-contamination of hair by saliva and urine under commercial husbandry conditions may also interfere with the validity of HCC in this species.