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.
Highlights
| INTRODUCTIONGlucocorticoid (GC; cortisol/corticosterone) secretion from the hypothalamus–pituitary–adrenal axis (HPA‐axis) follows an endogenous circadian rhythm
Day 2010:30 14:30 11:45POST2 Day 21–23 10:30 14:30 CS Newcomer 6 SF Resident 6 CH Resident 6Note: Number and timing of saliva samples of the newcomer CS and the residents SF and CH in the four transport phases (PRE, POST1, Introduction, POST2), as well as timing of the transport phases in relation to Day 0
The present study assessed the diurnal variation in salivary cortisol in captive African elephants during routine management and in relation to a potential stressor to evaluate to what extent acute stress may affect diurnal cortisol patterns
Summary
Glucocorticoid (GC; cortisol/corticosterone) secretion from the hypothalamus–pituitary–adrenal axis (HPA‐axis) follows an endogenous circadian rhythm. Fecal and urinary cortisol metabolites represent integrative measures of cortisol secretion and, concerning the African elephant, occur in the sample after a relatively long lag time of up to 38 hr in feces and 4.5 hr in urine (Ganswindt, Palme, Heistermann, Borragan, & Hodges, 2003). They are, not suitable to measure acute responses and are of limited use for understanding the diurnal variation of cortisol secretion. Saliva can be collected minimally invasively and repeatedly from captive elephants provided that the animals are habituated to sampling through positive reinforcement training
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