Abstract:
The occurrence of stress-inducing factors in captive crocodilians is a concern, since chronic stress can negatively
affect animal health and reproduction, and hence production. Monitoring stress in wild crocodiles could also be
beneficial for assessing the state of health in populations which are potentially threatened by environmental
pollution. In both cases, a non-invasive approach to assess adrenocortical function as a measure of stress
would be preferable, as animals are not disturbed during sample collection, and therefore sampling is
feedback-free. So far, however, such a non-invasive method has not been established for any crocodilian species.
As an initial step,we therefore examined the suitability of two enzyme-immunoassays, detecting faecal glucocorticoid
metabolites (FGMs) with a 11β,21-diol-20-one and 5β-3α-ol-11-one structure, respectively, for monitoring
stress-related physiological responses in captive Nile crocodiles (Crocodylus niloticus). An adrenocorticotropic
hormone (ACTH) challenge was performed on 10 sub-adult crocodiles, resulting in an overall increase in
serum corticosterone levels of 272% above the pre-injection levels 5 h post-injection. Saline-treated control
animals (n=8) showed an overall increase of 156% in serum corticosterone levels 5 h post-administration. Faecal
samples pre- and post-injection could be obtained from three of the six individually housed crocodiles,
resulting in FGMconcentrations 136–380% above pre-injection levels, always detected in the first sample collected
post-treatment (7–15 days post-injection). FGM concentrations seem comparatively stable at ambient temperatures
for up to 72 h post-defaecation. In conclusion, non-invasive hormone monitoring can be used for
assessing adrenocortical function in captive Nile crocodiles based on FGM analysis.
