A broad-selective enzyme immunoassay for non-invasive stress assessment in African Penguins 1 (Spheniscus demersus) held in captivity

We applied a direct competitive immunoassay for measuring corticosterone and glucocorticoid metabolites in faeces (FGMs) as a non-invasive tool for monitoring the stress response of African penguins (Spheniscus demersus) held in captivity in a zoological facility. The developed assay, validated in-house, proved to be rapid (the test could be completed in 90 minutes), sensitive (LOD for corticosterone 0.0002 mg/l, dynamic range 0.00075–0.075 mg/l) and broad-selective, as it cross-reacted with the major corticosteroids, thus allowing the detection of excreted FGMs resulting from a biological stressor. Matrix interference, due to components of faecal samples, was overcome by diluting sample extracts (1 + 4 or 1 + 9, depending on the sample). The assay enabled us to investigate the response to stress in five animals – three adult males and two adult females – over a period of 30 hours, and to identify the peak of FGM production as being 7–10 hours after the stressful event