Fecal Glucocorticoid Metabolites as Biomarkers in Equids: Assay Choice Matters

Abstract

Free ranging animals are exposed to environmental, demographic, and ecological challenges over time, which can affect their health and fitness. Non-invasive biomarkers can provide insight into how animals cope with these challenges and assess the effectiveness of conservation management strategies. We evaluated how free ranging ponies (Equus ferus caballus) on the Carneddau Mountain range, North Wales respond to 2 stimuli: an acute stressor of an annual roundup event in November 2014, and spatial and temporal variation in ecological factors in 2018. We evaluated fecal glucocorticoid metabolites using 2 enzyme immunoassays (EIAs): an 11-oxoetiocholanolone EIA (measuring 11,) and a corticosterone EIA. The former assay has been validated in equids, whereas there is limited evidence for the suitability of the latter. We used an additional parent testosterone EIA to measure fecal androgen metabolites in response to the ecological challenges. Following the roundup, the metabolite concentrations measured by the 2 glucocorticoid EIAs were not correlated. The 11,17-DOAs were elevated from the second day following the roundup and then slowly returned to pre-round levels over the next 2 weeks. In contrast, the metabolites measured by the corticosterone assay showed no response to the roundup. For the ecological data, all 3 assays detected a positive correlation between metabolites and social group size in males but not in females. The metabolite concentrations measured by the testosterone and corticosterone assays were highly correlated and were temporally associated with the onset of the breeding season, whereas the 11,17-DOAs were not. The co-variance of metabolites measured by the corticosterone and testosterone assays, and the lack of an acute response in the corticosterone assay to the roundup, suggests that metabolites detected by the corticosterone assay were not primarily associated with increased glucocorticoid production. We recommend using well-validated fecal biomarker assays of hypothalamuspituitary-adrenal axis activity to evaluate and compare the effect of different management interventions and environmental change.

Welfare assessment of horses ridden in the Costa Rica National Horse Parade

“…Before castration, these authors report median concentrations of 10.5 nmol/kg feces (3.19 ng/g 1 ) and after castration values increased to 26.2 (7.97 ng/g 1 ) and 50 nmol/kg feces (15.22 ng/g 1 ). In addition, Hinchcliffe et al 2021 found that fecal glucocorticoid metabolites were elevated from the second day following a stressor (a roundup) and then slowly returned to basal levels over the next 2 weeks. Franceschini et al…”

Rewilded horses in European nature conservation – a genetics, ethics and welfare perspective

“…While strict legal enforcement controlling human-animal interactions is necessary to avoid abuse of companion or farm animals (Webster, 2001;Verga and Michelazzi, 2009), these regulations pose challenges with free-roaming animals in more extensive environments (Veit and Browning, 2021). Indeed, while domestic horses habituated to regular veterinary interventions can manage stress well (Carroll, et al 2022), captures and veterinary care may cause acute stress levels in free-roaming horses (Hinchcliffe et al, 2021, Scasta et al, 2021, and endanger their lives (e.g., injuries caused by fear (Winther, 2006)). Medical treatments may also harm horses, (e.g., due to toxicities or reduced immunity, Ang et al 2022;Flood and Stewart, 2022) affecting their shortand long-term life-quality (Rombke et al 2010;van Klink et al 2015).…”