Cortisol is a key biomarker of stress and hypothalamic-pituitary-adrenal (HPA) axis activity in an organism. Different biological samples are used for measuring cortisol levels, such as blood, saliva, milk, urine, faeces, and hair. Blood plasma or serum cortisol measurements are widely applied to quantify acute stress response in farm animals, but stress sampling and rapid hormonal changes can undermine accuracy in results. Saliva has proven to be a reliable alternative sample for assessing free cortisol, offering a less stressful approach with minimal triggering of the stress response. Cortisol determination in milk is a non-invasive method of limited applicability for lactating ruminants, though physiological parameters such as milk yield and stage of lactation can influence its interpretation. Concentrations of cortisol in urine reflect the cumulative cortisol secretion over time, making it a valuable indicator of chronic stress, though research on small ruminants remains limited. Similarly, faecal cortisol metabolites offer a non-invasive means of assessing adrenal activity with delayed but integrated hormonal fluctuations. Hair and wool analysis provide insight into long-term stress exposure, though factors such as seasonal variation and local synthesis complicate its application. This review highlights the strengths and challenges associated with different cortisol sampling methods, emphasising the importance of multiple biological sample approaches for accurate welfare assessments in ruminants.
Šimunec et al. (Thu,) studied this question.