Seasonal rhythms of salivary cortisol secretion in captive Asian elephants (Elephas maximus)

Abstract

Salivary cortisol has been recently used to assess welfare of captive and free-ranging animals. However, rhythms of cortisol secretion may vary annually and thus, it is necessary to take into account these rhythms when evaluating the physiological significance of fluctuations of this hormone throughout the year as stress indicator in animals. Here, we analyze monthly differences in cortisol secretion in Asian elephants (Elephas maximus) during a year. Saliva samples of eight adult female Asian elephants were collected and analyzed using Radioimmunoassay. Results revealed an overall seasonal pattern of salivary cortisol secretion and significant differences in cortisol concentration among months were found. Overall, the highest cortisol levels were recorded in October, and then decreased until reaching the lowest concentration in April. However, some individual variations were found respect this annual overall trend. The occurrence of this annual pattern of cortisol secretion should be taken into account when using cortisol as a tool to assess animal welfare in captive animal at zoological parks, as well as it opens new questions to further analyze this pattern and its variations, as well as the endogenous mechanisms controlling it.