Measurement of Salivary Cortisol in Two New World Primate Species

SIMPLE SUMMARY: Glucocorticoids (GCs) play a vital role in the body’s response to stress. Therefore, scientists use GC level measurements as a valuable tool to understand the well-being of animals in behavioral, conservation, and welfare research. GC levels can be measured from different sample types, one of them being saliva. Saliva samples are especially useful because they can be collected rather easily and in a non-invasive manner. The aim of this study is to validate a method to measure salivary GCs, i.e., an enzyme immunoassay, in two monkey species: capuchin monkeys and squirrel monkeys. Individuals of both species were trained to provide saliva samples. Using high-pressure liquid chromatography, we confirmed that two main GCs, cortisol, and cortisone, are present in the saliva of these species and that they can be detected by the enzyme immunoassay. We further verified the biological validity of the assay in the two species by showing that it can track the decrease in cortisol levels throughout the day, which is typical in these monkeys. Our findings support the usefulness of the enzyme immunoassay to measure salivary cortisol levels in these non-human primate species and highlight its potential as a valid tool in research and welfare assessment. ABSTRACT: Glucocorticoids (GCs) are mammalian steroid hormones involved in a variety of physiological processes, including metabolism, the immune response, and cardiovascular functions. Due to their link to the physiological stress response, GC measurement is a valuable tool for conservation and welfare assessment in animal populations. GC levels can be measured from different matrices, such as urine and feces. Moreover, especially in captive settings, measuring GCs from saliva samples proved particularly useful as those samples can be collected non-invasively and easily from trained animals. Salivary GC levels can be measured using a variety of analytical methods, such as enzyme immunoassays. However, it is crucial to validate the analytical method for each specific application and species when using a new matrix. Using high-pressure liquid chromatography and a cortisol enzyme immunoassay, we show that the main glucocorticoids secreted in the saliva of squirrel monkeys and brown capuchin monkeys are cortisol and cortisone. Our biological validation found the expected salivary cortisol level to decline throughout the day. Our findings support the reliability of salivary cortisol measurements and their potential to be used as a valid tool in research and welfare assessment for these non-human primates.