Hair Cortisol: A Biomarker of Chronic Stress in Animals and Its Association With Reproduction

Hair cortisol concentration (HCC) is increasingly used as a biomarker for chronic stress, reflecting months to years of hypothalamic-pituitary-adrenal (HPA) axis activity based on hair growth rates and lengths. It is applied to various groups including domestic, wild, and captive animals, as well as humans with trauma or PTSD, offering a retrospective measure of chronic HPA activity that is not influenced by acute stressors or daily fluctuations. Chronic stress, as indicated by HCC, is significant in its impact on animal fertility, with HPA axis activation leading to reduced testosterone in males and potential disruption of ovulation in females due to suppressed Leutinizing hormone (LH) secretion. Therefore, HCC analysis serves as a critical tool for evaluating animal welfare by assessing the HPA-HPG axis.