Comparison of methods for faecal hormone preservation and analysis in African savanna elephants under field conditions.

Noninvasive faecal hormone analyses can provide valuable information on the physiological state of wild animals and how they respond to ecological changes or anthropogenic disturbances. However, preservation techniques to prevent hormone alteration can be problematic, and not all are field friendly. We compared five processing methodologies to preserve samples for faecal glucocorticoid, progestagen and thyroid hormone metabolites. Samples were collected from adult zoo Africa savanna elephants (Loxodonta africana) (one male, four females) immediately after defecation. Subsamples were then subjected to five preservation methods: lyophilisation (LYO) (considered the gold standard), dehydration, solid-phase extraction (SPE) and two ethanol extraction methods-with and without being immediately dried down. Faecal glucocorticoid, progestagen and thyroid hormone metabolites were quantified by validated enzyme immunoassays. After 7 days at room temperature (to emulate shipping conditions), faecal glucocorticoid metabolite concentrations were lower for all methods compared to LYO. For thyroid hormone metabolite concentrations, the dehydration process resulted in higher concentrations compared to LYO, whereas with SPE, concentrations were lower. For faecal progestagen metabolite concentrations, there were no discernible differences across methods. Based on these results, we recommend ethanol extraction followed by immediate sample desiccation, a method that combines technical simplicity with the advantage of ambient temperature sample storage and transportation. Nevertheless, each investigator should consider the best method for the research question, field conditions, budget, equipment accessibility and shipping requirements, especially as results can vary by species and assay used. With growing interest in assessing animal welfare, validating field methods for noninvasive hormone monitoring is essential.