Allostatic Load Index Effectively Measures Chronic Stress Status in Zoo-Housed Giraffes

Abstract

For giraffes, few standardized methods exist for quantifying chronic stress. Allostatic load index is quantified from a panel of multi-system stress biomarkers to estimate cumulative stress. Our objective was to determine whether a panel of biomarkers selected for their role in allostatic load would reflect the number of documented stress events experienced by giraffes. Cortisol, DHEA-S, cholesterol, non-esterified fatty acids (NEFA), and fructosamine were determined in serum samples from zoo-housed giraffes (n = 18). These were correlated with the overall number and frequency of ZIMS-documented stress events experienced prior to blood collection. We also compared giraffes grouped by high vs. low total stress events and event frequencies. Giraffes experiencing higher total stress events tended to have 1.65-fold greater (p < 0.10) serum cortisol, had 1.49-fold greater (p < 0.05) serum fructosamine, and had 3.9-fold greater (p < 0.05) allostatic load. Giraffes experiencing higher stress-event frequency had 2.4-fold greater (p < 0.05) serum NEFA. Correlations for individual biomarkers with individual stress event categories were inconsistent, but DHEA-S (r = −0.44), cortisol/DHEA-S (r = 0.49), fructosamine (r = 0.54), and allostatic load (r = 0.49) correlated (p < 0.10) with total stress events. These findings indicate that the allostatic load index robustly reflected total cumulative stress events for these giraffes and was more consistent than the individual biomarkers used for its calculation. We conclude that allostatic load index is a promising tool for assessing stress in captive giraffes, although revision of the biomarker panel is warranted.