Saliva sampling to assess cortisol levels in unrestrained common marmosets and the effect of behavioral stress

We report a method for taking saliva samples from unrestrained, captive marmosets (Callithrix jacchus) to assess levels of free cortisol. Saliva samples can be obtained reliably, without any habituation, by encouraging the marmosets to lick and chew a cotton-wool bud coated in banana. Saliva is thus left on the bud. We also tested sweetened fruit-drink crystals and a number of other substances, but none of these attracted all of the marmosets, and even flavors that were effective once soon lost their attraction. The presence of banana in the samples collected was found to lower the measured concentration of cortisol; however, as shown in samples taken with and without the banana coating on the bud, it did so in a linear and consistent way, and did not vary significantly among subjects. Therefore, a simple conversion factor could be applied to correct for the presence of banana. A first experiment showed that the marmosets exhibited a rise in salivary cortisol levels in response to social isolation. A second experiment showed elevation of cortisol during a period when the marmosets were disturbed by increased human activity and noise levels in the building in which they were housed. Hence, this method of saliva sampling is a convenient, noninvasive means of assessing cortisol levels in marmosets.