Evaluating Allostatic Load: A New Approach to Measuring Long-Term Stress in Wildlife

Abstract

Animal welfare, conservation, and stress assessment are all critical components of species survival. As organisms experience stressors, they accumulate physiologic dysregulation, leading to multiple negative health outcomes. This brief review suggests measuring the degree of stress-induced damage, known as allostatic load, and then using allostatic load to evaluate changes implemented to improve animal welfare and conservation efforts. Over the past two decades, human clinical research has developed multiple allostatic load indices constructed from composites of neuroendocrine, cardiovascular, metabolic, and immune biomarkers. These indices are designed to estimate allostatic load in hopes of ameliorating or even negating damaging effects of stress. Among humans, allostatic load is associated with a variety of factors such as age, sex, stressful experiences, personality, social position, and early life history. Despite conservation of stress responses throughout mammalian species, reported allostatic load indices for animals are rare. Because many zoo researchers and field scientists already collect data on multiple biomarkers, constructing allostatic load indices may be a relatively affordable, easily implemented, and powerful tool for assessing relative risks of morbidity and mortality within wildlife. As an example, in a study among zoo-housed gorillas, an allostatic load index constructed using seven biomarkers was associated significantly with age, sex, stressful experiences, rearing history, markers of poor health, and mortality risk. Such results evidence that allostatic load is as applicable to animal populations as it is to humans. By using allostatic load as a predictive tool, human caretakers will be better informed of individuals at greatest risk for health declines. Most importantly, allostatic load may provide earlier opportunity for preemptive care while contributing a transformational tool to animal welfare research. Additionally, allostatic load may be compared between individuals and groups within the same population and allow comparisons of health between and across populations, consequently informing habitat and population protection efforts.

Life expectancy, family constellation and stress in giant mole-rats ( Fukomys mechowii )

“…The binding of ACTH to ACTH receptors expressed in adrenal glands induces cortisol secretion [19]. Although glucocorticoids are primarily involved in restoring energy homeostasis, chronic exposure to elevated glucocorticoid levels can increase allostatic load, a measure of stress-induced damage, leading to health impairments across various animal taxa [20][21][22][23][24][25].…”

Allostatic load in the context of disasters

“…AL was originally described in people, which is undoubtedly the most complex organic system in which to try to understand mechanisms of action. AL also has been employed to assess health status and predict disease risk in captive non-human primates, including gorillas ( Edes et al, 2018 , Edes et al, 2020 ) and lemurs ( Seeley et al, 2021 ) and may have potential for much broader application in animal husbandry. However, mechanistic underpinnings for AL have yet to be comprehensively described.…”

The rat cumulative allostatic load measure (rCALM): a new translational assessment of the burden of stress

“…To better assess the cumulative effects of chronic or recurrent stress and to detect potentially sub-clinical symptoms of stress, a panel of biomarkers is more sensitive than a single marker. The value of assessing multiple biomarkers, including primary and secondary mediators, may improve high-risk detection as well as intervention strategies to promote health and well-being in humans [42] and enhance resilience to chronic stresses in wildlife [43]. Multivariable tools, such as the rCALM increase the ability to identify individuals at risk for developing complex diseases that influenced by stress.…”