Differences between horses (Equus caballus) displaying oral and locomotor stereotypies in their responses to a stable mirror.

Overview

• This study examined how horses showing different types of stereotypic behaviors (repetitive, invariant behaviors) respond to a stable mirror that simulates the presence of another horse.
• It compared horses exhibiting locomotor stereotypy (box-walking), oral stereotypy (crib-biting), and horses without stereotypic behaviors to understand if social motivation varies among these groups.

Background and Context

• Stereotypic behaviors are repetitive, seemingly purposeless behaviors often seen in captive or domesticated animals, linked to stress or inadequate environments.
• Different forms of stereotypies may have distinct causes or motivations; for example, locomotor stereotypies (like box-walking) might be socially motivated, while oral stereotypies (like crib-biting) might not.
• The domestic horse (Equus caballus) serves as a model species to study these behaviors within ungulates (hoofed animals).

Study Design and Methods

• Subjects: 16 horses split into three groups:
  • Box-walking group (locomotor stereotypy; n=6)
  • Crib-biting group (oral stereotypy; n=5)
  • Non-stereotypic control group (n=5)
• Setup:
  • Phase 1: 24-hour baseline with no mirror.
  • Phase 2: 24-hour exposure to a large stable mirror (1 × 1.5 meters) intended to simulate presence of a conspecific (another horse).
  • Phase 3: 24-hour post-mirror phase with mirror removed.
• Data collection:
  • Measured behavioral responses: stereotypy frequency and duration.
  • Orientation: how much time horses spent facing the mirror.
  • Ear and head/neck movements, which can indicate social/affiliative behavior or frustration.

Key Findings

• Box-walking horses showed a significant reduction in their stereotypic locomotor behavior when the mirror was present.
• This reduction persisted even after the mirror was removed.
• Crib-biting horses did not alter their oral stereotypy behavior in response to the mirror.
• Both box-walkers and non-stereotypic horses spent more time oriented toward the mirror than crib-biters, suggesting greater interest or attention.
• Despite increased time facing the mirror, box-walking horses did not show more affiliative social signals (ear or head/neck movements) while the mirror was present or more frustration behaviors when it was removed compared to other groups.
• Unexpected differences in mirror responses emerged among the groups beyond the main predictions, indicating complexity in behavioral reactions.

Interpretation and Implications

• The reduction in box-walking with mirror presence suggests that this locomotor stereotypy might be linked to social motivation or the lack of social contact.
• Crib-biting behavior appears less influenced by social stimuli, indicating differing underlying mechanisms for oral stereotypy.
• The mirror might serve as a partial social substitute for box-walking horses, temporarily alleviating the drive to perform stereotypic locomotor behavior.
• The absence of increased affiliative signals or frustration behaviors around mirror exposure or removal implies that the mirror’s effects are subtle and complex.
• Additional research with larger sample sizes and controls is necessary to confirm these preliminary findings and clarify the social motivation behind different stereotypies.

Conclusion

• This study provides initial evidence that horses exhibiting locomotor stereotypy (box-walking) respond differently to simulated social stimuli (mirror) compared to horses with oral stereotypy or no stereotypy.
• The findings support the idea that different stereotypies may have heterogeneous causes and motivations, particularly relating to social needs in ungulates.
• Future studies should build on this work to better understand how environmental enrichment such as mirrors may impact horse welfare and management.