# Relationship Between Physical Activity, Blood Cortisol Levels and Innate Immune Response in Common Bottlenose Dolphins (Tursiops truncatus) in a Controlled Environment

## TL;DR

This study explores how physical activity affects cortisol levels and immune function in captive bottlenose dolphins, revealing a strong link between stress hormones and immune response.

## Contribution

The study provides new insights into the relationship between cortisol, physical activity, and innate immune function in cetaceans.

## Key findings

- Physical activity significantly increased cortisol levels by 122% in dolphins.
- Phagocytic activity in granulocytes and monocytes decreased during periods of physical activity.
- A negative correlation was found between cortisol levels and immune cell function.

## Abstract

Cortisol has been extensively studied in captive cetaceans, but its relationship to immune function remains poorly understood. An apparently asymptomatic individual exposed to certain exogenous or endogenous factors could experience an increase in blood cortisol levels, which could alter the function of immune system cells and influence its well-being. To better understand these mechanisms and their implications for animal welfare, this article will evaluate the relationship between blood cortisol levels and their influence on the function of the innate immune system in captive bottlenose dolphins.

This study investigates the effects of physical activity on serum cortisol levels and phagocytic capacity of the innate immune system in eight common bottlenose dolphins under human care. Analysis of 8 pairs (16 samples) revealed a significant increase in cortisol during periods of physical activity (mean increase of 1.27 µg/dL, 122% elevation), accompanied by decreased phagocytosis in granulocytes (92% reduction) and monocytes (52% reduction). Statistical analyses demonstrated consistent negative correlations between cortisol levels and phagocytic function, suggesting that physical activity influences hypothalamic–pituitary–adrenal axis activation and, consequently, innate immune system function. The male showed an attenuated cortisol response, but maintained monocyte sensitivity. These findings highlight the complex interplay between the neuroendocrine cortisol response and immune function in cetaceans, for the management and evaluation of animals under human care. A multi-method statistical framework incorporating Bayesian analysis, bootstrapping, and traditional approaches ensured robust inference despite limited sample size.