Non-invasive monitoring of glucocorticoid metabolites in brown hyaena (Hyaena brunnea) feces

Abstract

The brown hyaena (Hyaena brunnea) is the least known of the large predators of southern Africa. The current IUCN status of the brown hyaena is “Near Threatened”, and there are conservation concerns related to a general lack of biological knowledge of the species. For instance, a better knowledge of the responses to environmental and social stressors would improve our abilities to sustainably manage brown hyaena populations in both captive and free-ranging environments. We conducted adrenocorticotrophic hormone (ACTH) challenges in one female and one male adult brown hyaena at Lion Park Zoo, South Africa, to validate measurements of glucocorticoid metabolites (GCM) in brown hyaena faeces via an enzyme linked immunoassay (EIA). We also measured gastrointestinal transit times (GIT times) and the GCM degradation in faeces left in ambient temperature for up to 32 hours to more reliably assess the use of this assay as a tool for non-invasive glucocorticoid measurements. Intramuscular injections of synthetic ACTH yielded GCM levels of 388% (female) and 2682% (male) above baseline with peak increases occurring 25- 40 hours post injection. The time delay of faecal GCM excretion approximately corresponded with food transit time in the brown hyaenas. Faecal GCM levels declined significantly over time since defecation. Our results provided a good validation that faecal GCM's accurately reflects circulating glucocorticoid stress hormones in brown hyaenas, but we highlight that samples have to be frozen immediately after defecation to avoid bias in the measurements due to bacterial degredation.