The Effects of Androstenone on the Plasma Serotonin, β-Endorphin, and Cortisol Concentrations in Thoroughbred Horses.

Yeonju Choi,Minjung Yoon

doi:10.3390/ani11061694

Abstract

Simple SummaryThe development of horse managing tools is needed to prevent accidents and to improve welfare for domestic horses because the safety hazards for people who are exposed to horses are well documented. Androstenone, a pheromone secreted from boars, changes the behavior of dogs to become less excited. In horses, a previous study showed that a specific receptor for androstenone was expressed in the vomeronasal organ and nasal cavity. Horses treated with androstenone also showed more compliant behaviors. Thus, this study was conducted to investigate the mechanism of androstenone for changing horse behaviors. The change in the plasma concentrations of serotonin, β-endorphin, and cortisol in response to the treatment of androstenone was evaluated using an immunoassay. The results of this study demonstrated that androstenone may control the neuroendocrine system of horses, resulting in behavioral changes. This is the first work that studies the mechanism of pheromone treatment in horses and can be applied for further study about the effect of pheromone therapy on horses.Androstenone influences the changing behaviors of animals. Previous studies discovered that an androstenone receptor was expressed in horses and treatment with androstenone induced horses to be more compliant. As changes in the level of neuroendocrine factors result in animal behavioral changes, the objective of the study was to monitor the changes in the concentrations of 5-HT, β-endorphin, and cortisol in response to androstenone. Eight thoroughbred horses (five mares and three geldings) were treated with androstenone diluted in jojoba oil (10 µg/mL) and only oil for a control cross-overly. A handler applied the treatments to the horses′ nostril and rubbed for 5 s. Blood samples were collected before, 15, 30, and 60 min after each treatment. The concentrations of each neurotransmitter were analyzed by enzyme-linked immunosorbent assay. The concentrations of each neurotransmitter after the treatment were compared to its baseline concentration. The concentration of 5-HT of the androstenone-treated horses remained consistent throughout the experiment, while the concentration of the control group significantly decreased over time. The plasma concentration of β-endorphin in the androstenone-treated group also remained constant, whereas the concentration increased in the control group. Cortisol levels did not change in either the treated or untreated groups. An androstenone treatment triggers changes in the secretion of 5-HT and β-endorphin in horses.

Highlights

Hormones and/or neurotransmitters act on the nervous system to regulate physiological responses and behavioral changes [1,2]
We recently reported an expression of the androstenone specific receptor (OR7D4) in the vomeronasal organ and nasal cavity of horses [8], indicating that horses have an ability to sense androstenone
The behavioral changes of horses, which see them become more compliant to handlers, caused by pheromone treatment may have a correlation with the 5-HT secretion

Summary

Introduction

Hormones and/or neurotransmitters act on the nervous system to regulate physiological responses and behavioral changes [1,2]. 5-HT is involved in the social behaviors of many animal species such as hamsters [9], rats [12], mice [13], dogs [14], and humans [15]. These studies show that high levels of 5-HT promote social interaction and decrease aggression in animals. The results of previous studies led us to hypothesize that the concentration of plasma 5-HT could be induced by androstenone treatment

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