# Addressing Combative Behaviour in Spanish Bulls by Measuring Hormonal Indicators

## TL;DR

This study finds that hormone levels in young bulls can predict their aggressive behavior as adults, which is useful for selecting fighting bulls.

## Contribution

The study introduces hormone testing in calves as a reliable method to predict combative behavior in mature fighting bulls.

## Key findings

- Serotonin and dopamine levels in calves correlate with aggressive behavior in adult bulls.
- Testosterone levels were not correlated with aggressiveness in fighting bulls.
- Hormone measurements in calves can reliably predict combativeness scores in mature bulls.

## Abstract

Aggressiveness in fighting bulls is a natural characteristic of this breed, but little is known regarding it physiological mechanisms. Hormones such as serotonin, dopamine and testosterone are known to be involved in the development of aggressive behaviour. This study determines that serotonin and dopamine levels are correlated with combative behaviour, and its determination in calves is a useful indicator for the selection of combative bulls.

The fighting bull is characterised by its natural aggressiveness, but the physiological mechanisms that underlie its aggressive behaviour are poorly studied. This study determines the hormonal component of aggressiveness in fighting bulls by analysing their behaviour during a fight and correlating it to their serotonin, dopamine and testosterone levels. We also determine whether aggressive behaviour can be estimated in calves. Using 195 animals, samples were obtained when the animals were calves and after 5 years. Aggressiveness scores were obtained by an observational method during bullfights, and serotonin, dopamine and testosterone levels were determined in all animals using validated enzyme immunoassay kits. The results revealed a strong correlation of serotonin and dopamine levels with aggressiveness scores in bulls during fights, but no correlation was found with respect to testosterone. These correlations led to established cut-off point and linear regression curves to obtain expected aggressiveness scores for calves at shoeing. There were no significant differences between the expected scores obtained in calves and the observed scores in bulls. Therefore, this study demonstrates that hormone determination in calves may be a great indicator of combativeness in bulls and can reliably be used in the selection of fighting bulls.