Can we assess neuroticism in horses? A study on a novel behavioural test

Abstract

Neuroticism is one of the five personality traits described in the Five-Factor Model and is associated with emotional instability and behavioural rigidity. It reflects an individual’s sensitivity to negative emotions, resulting in repetitive behavioural responses aimed at avoiding novelty and the unknown. Although this trait has been assessed in horses through questionnaires, no behavioural test had been developed to measure it objectively. This study aimed to propose a novel behavioural test to assess neuroticism in horses based on patterns of food-choice repetition. Fifteen adult mixed-breed mares were tested over five consecutive days in a familiar arena. The test comprised two phases: (1) food recognition and (2) assessment of repetitive patterns in food consumption. Five food types (carrot sticks, carrot cubes, chicory, apple semicircles, and triangular apple pieces) were placed in five divisions of a table. In phase 1, mares underwent five consecutive three-minute sessions, each presenting a single food type. In phase 2, all five foods were presented simultaneously in a fixed arrangement, and each mare completed one five-minute session per day for four days. The sequence in which each food item was consumed was recorded manually. A repetition-based "interday score" was calculated for each mare to quantify behavioural consistency across days. Scores ranged from 32 to 138 points, indicating individual variability in food-choice patterns. To evaluate whether the score represented a new personality trait, principal component analyses were conducted using behavioural data from three validated personality tests (open field, novel object, and startle tests). The interday score did not load with any component extracted from these tests, suggesting it captured a distinct behavioural dimension. This new test generated diverse, consistent response patterns among individuals and appears to assess a personality trait related to neuroticism; however further validation against questionnaires or other tests that measure (or intent to) neuroticism are still needed. Nonetheless, the findings offer a novel behavioural approach to better understand equine personality.