Diurnal variation of salivary cortisol in captive African elephants (Loxodonta africana) under routine management conditions and in relation to a translocation event

Abstract

The present study assessed the diurnal variation in salivary cortisol in captive African elephants during routine management (baseline) and in relation to a potential stressor (translocation) to evaluate to what extent acute stress may affect diurnal cortisol patterns. Under baseline conditions, we collected morning and afternoon saliva samples of 10 animals (three zoos) on different days in two study periods (n = 3-10 per animal, daytime and period). Under stress conditions, we sampled the transported cow (newcomer) and the two cows of the destination zoo before and after the transport in the morning and afternoon (n = 3-9 per animal, daytime and transport phase), as well as after the first introduction of the newcomer to the bull (n = 1 per animal). Cortisol was measured in unextracted samples by enzyme immunoassay. Under baseline conditions, we observed the expected diurnal variation with higher cortisol levels in the morning than in the afternoon. Under stress conditions, neither a significant difference between pre-and posttransport, nor between morning and afternoon levels was found. The percentage difference between morning and afternoon cortisol after the transport, however, was remarkably lower than before the transport in the newcomer potentially indicating a stress response to familiarization. Saliva samples taken immediately after the introduction of the newcomer to the bull revealed a marked cortisol increase. Our findings indicate that stressors may disturb the diurnal cortisol rhythm. Furthermore, provided that samples can be collected promptly, salivary cortisol is a useful minimally invasive measure of physiological stress in the African elephant.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Effects of Positive Reinforcement Training and Novel Object Exposure on Salivary Cortisol Levels under Consideration of Individual Variation in Captive African Elephants (Loxodonta africana)

“…Sampling occurred at fixed daytimes to minimize the influence of the diurnal rhythm of cortisol secretion [ 30 ]. The time of day of sampling differed between zoos due to differences in management routine but was consistent within zoos during the whole study periods: 13:00 in Erfurt, 14:00 in Wuppertal, 18:00 in Kronberg.…”

“…We measured SACort with a microtiter plate enzyme immunoassay (EIA; [ 104 ]), which was used successfully for the assessment of physiological stress via SACort analysis in a number of other species [ 94 , 105 ]. We also biologically validated and successfully applied this assay previously to assess the diurnal rhythm of cortisol secretion in our study subjects [ 30 ]. All samples were measured in duplicate as described in detail in [ 30 ].…”

“…We also biologically validated and successfully applied this assay previously to assess the diurnal rhythm of cortisol secretion in our study subjects [ 30 ]. All samples were measured in duplicate as described in detail in [ 30 ].…”

“…Feces, e.g., [ 26 , 27 ], and blood, e.g., [ 21 , 24 ], are the most frequently used sampling matrices for GC measurements in African zoo elephants. Saliva has also been used a few times in this species as a GC sampling matrix [ 28 , 29 , 30 , 31 ] and can be collected minimally invasively [ 32 ] from captive African elephants as part of routine training, as the mouth cavities of the animals are regularly inspected. The animals can, therefore, be easily habituated to saliva collection, which minimizes the abovementioned risk of causing GC elevations by sampling itself.…”

Nutritional influences on enzyme activities in saliva of Asian and African elephants

“…Until now, composition of Asian and African elephant saliva has been rarely studied (Raubenheimer et al 1988;Menargues et al 2012;Marcilla et al 2012;Illera et al 2014;Edwards et al 2019;Plangsangmas et al 2020;Hambrecht et al 2020). This study is based on a previous comparative investigation of salivary enzyme activities in Asian and African elephants, which collected saliva only once a day (Boehlke et al 2016).…”