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

A giraffe’s blood may carry clues to years of demanding experiences. A move, an illness or a veterinary immobilisation can each challenge the body. Measuring one stress hormone captures only part of that response, prompting researchers to ask whether several physiological signs together could better reflect an animal’s accumulated history.

Haley Beer, Lisa Karr, Trenton Shrader and Dustin Yates examined stored blood samples from 18 giraffes at Omaha’s Henry Doorly Zoo and Aquarium. They combined five blood measurements with body-condition scores into an index that counted unusually high or low values. They then compared that index with recorded illnesses, transport, immobilisations and pregnancies before the blood sample was taken.

The half of the giraffes with more recorded events had an index nearly four times higher than the other half. Individual blood markers gave a less consistent picture, and the index did not distinguish groups by their average number of events per year. This small, single-zoo comparison used thresholds derived from the same animals and did not test whether the score predicted future illness. It therefore offers a promising approach, not an established diagnosis of chronic stress. The central idea is to read several body systems together, alongside the giraffe’s history, rather than expect one hormone to tell the whole story.