Analysis of different biological matrices for glucocorticoid detection in wild Cervidae and Bovidae from Europe and North America: a review

Background: Stressful situations that trigger an acute stress response help animals to survive in the wild. In contrast, a prolonged stressful situation can have a negative effect on the animal’s health. The organism activates the HPA axis, which stimulates the adrenal cortex through an intricate network of responses. In response to the stimulation, the adrenal cortex releases glucocorticoids. Hormones and their metabolites are a good indicator of stress levels in wild animals and can be measured in many matrices such as blood, feces, urine, saliva and hair. Many studies have investigated the effects of various stressors such as anthropogenic influences, environmental and biological factors and predation on glucocorticoid levels in these non-invasive matrices. We provide an overview of the literature on this topic in wild Cervidae and Bovidae, focusing only on Europe and North America. Results: We reviewed the scientific literature published between 1979 and 2024 and found 77 papers studying the correlations between different stressors and glucocorticoid levels in wild ungulates. Most researchers used feces as the matrix of choice for analyzing glucocorticoid levels as well as enzymatic immunoassay (EIA) as the analytical method. In 41 of the 77 studies, the researchers validated the analytical method themselves (19 studies) or used the analytical method that had been previously validated by others on the studied species (22 studies). Conclusions: The increasing number of studies looking at stressful events in wild ungulates shows that researchers are interested in wildlife welfare and are making more effort to understand the biology of stress in wildlife.