Non-invasive assessment of adrenocortical function in captive Nile crocodiles (Crocodylus niloticus)

Abstract

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 noninvasive approach to assess adrenocortical function as a measure of stress would be 2 preferable, as animals are not disturbed during sample collection, and therefore sampling is feedback-free due to the absence of capture and handling. So far, however, such a noninvasive 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 11,21-diol-20-one and 5-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 hours post-injection. Saline-treated control animals (n=8) showed an overall increase of 156% in serum corticosterone levels 5 hours postadministration. Faecal samples pre-and post-injection could be obtained from three of the six individually housed crocodiles, resulting in FGM concentrations 136-380% above preinjection levels, always detected in the first sample collected post-treatment (7-15 days postinjection). FGM concentrations seem comparatively stable at ambient temperatures for up to 72 hours post-defaecation. In conclusion, non-invasive hormone monitoring can be used for assessing adrenocortical function in captive Nile crocodiles based on FGM analysis.

Non-invasive assessment of glucocorticoid and androgen metabolite levels in cooperatively breeding Damaraland mole-rats (Fukomys damarensis)

“…Steroid hormones may be metabolised and excreted differently between sexes of the same species, resulting in differences in metabolite composition within the faeces (Touma et al, 2003(Touma et al, , 2004. Further, a number of studies demonstrated sex-related differences in fGCM concentrations in response to ACTH administration (Ganswindt et al, 2012(Ganswindt et al, , 2014LeRoux et al, 2016). For example, glucocorticoid levels in females can be affected by the oestrus cycle.…”

Non‐invasive assessment of adrenocortical function as a measure of stress in the endangered golden langur

“…To calculate the EIA specific responses to the ACTH challenge, we set the sample collected from each individual on the day of ACTH administration as 100% and all other values were expressed as a percentage of the respective value. To compare individual fGCM concentrations in the captive group, individual baseline levels for the two pet animals were calculated using an iterative process as described (Ganswindt, Myburgh, Cameron, & Ganswindt, ). Differences in fGCM concentrations between individuals and between groups were determined using a Kruskal‐Wallis One Way Analysis of Variance on Ranks with a post‐hoc pairwise multiple comparison (Dunn's Test) to isolate the individuals or groups that differed from the others in SigmaPlot for Windows versions 12.5.…”

Peer Review #1 of "Non-invasive monitoring of glucocorticoid metabolite concentrations in urine and faeces of the Sungazer (Smaug giganteus) (v0.1)"

“…Understanding species-specific differences and individual variability in faecal and urinary defecation rates are important for a number of reasons. Firstly, the infrequent and extended excretion rate of urinary and faecal material in reptiles may complicate data interpretations (Ganswindt et al, 2014). Furthermore, the movement of urine into the cloaca (urodeum) before moving into the intestines, where urinary and faecal material can be excreted in unison (Singer 2003), can further complicate the distinction between matrix-specific retention time and steroid hormone metabolite excretion routes.…”

“…However, some more recent studies attempting to understand the physiological response inherent in reptiles to environmental stressors have already opted for non-invasive hormone monitoring in reptiles, e.g. in Nile crocodiles (Crocodylus niloticus, Ganswindt et al, 2014), the three-toed box turtle (Terrapene carolina triunguis, Rittenhouse et al, 2005), the green anole (Anolis carolinensis, Borgmans et al, 2018) or the green iguana (Iguana iguana, Kalliokoski et al, 2012).…”