The tail-tale of stress: an exploratory analysis of cortisol levels in the tail-hair of captive Asian elephants

Abstract

Background Assessment of physiological states by measuring biomarkers, such as cortisol, has significantly contributed to the monitoring of health, welfare and management of animals. Immunoreactive cortisol in hair (hC) has been used widely for deciphering ‘stressful’ past-events in various wild and captive animals. However, no such studies have been done in long-lived mammals. Methods In this first exploratory study in elephants, we assessed (i) tail-hair growth rate (TGR) and (ii) hC levels in tail-hair samples from six captive Asian elephants from two zoos in Japan for comparing hC levels with zoo-keepers’ records of distinct biological events over a c.0.5–2.0-year period. Tail-hair samples were cut into segments (based on monthly growth rate), pulverized or minced and a validated cortisol enzyme-immunoassay employed to measure hC levels. Results When the hC levels of all individuals were compared with the keepers’ records, a posteriori, most of the high hC levels were found to be associated with ‘stressful’ or distinct behavioural events such as pathological (anaemia, colic infection, skin infection, oral sores), psychosocial (reluctance in entering the enclosure, presence of a calf) and husbandry practice-related (contact trials/ space sharing) conditions, indicating that tail-hair indeed can be a potential ‘retrospective’ calendar of physiological health of an animal. Conclusions Our observations open up the possibility of using the tail-hair as an alternative matrix to reconstruct the physiological history of elephants.

Application of Felid Hair for Non-Invasive Tracking of Animal Reproductive Status and Adrenal Activity

“…The results in various species are somewhat inconsistent. It is believed that the level of hormones in the long hair of elephants (tail) [ 14 ] or orangutans [ 15 ] can reflect rather large time intervals, as in pinniped whiskers [ 16 ] or cetaceans baleen [ 17 ]. At the same time, the work carried out on adrenalectomized rats [ 18 ], followed by regular administration of corticosterone, showed that the level of corticosterone in their hair began to increase two weeks after the start of injections and began to decrease two weeks after they ended, thus reflecting a rather short life span of this hormone in animals.…”

Nailing it: Investigation of elephant toenails for retrospective analysis of adrenal and reproductive hormones

“…In elephants, keratin tissues such as toenails and tail hairs could allow evaluation of prolonged (multi-month) patterns of hormones, while providing a much broader timeframe than serum, faecal or urine sampling. While elephant tail hair has been investigated as a potential endocrine sample type for elephants, specifically for cortisol ( Pokharel et al., 2021 ), to our knowledge, no studies have evaluated elephant toenails as a potential sample matrix for any hormones. In ex situ populations, toenail trimmings are frequently removed from the distal part of the nail during routine foot care.…”