The Challenge of Defining Laterality in Horses: Is It Laterality or Just Asymmetry?
Abstract: The defining characteristic of laterality is the dominance of one side of the brain controlling specific functions of paired organs or on one side of the body. Structural and functional asymmetries are ubiquitous in horses and range from anatomical features (e.g., the length of long bones) to the gathering of sensory information (e.g., which eye is used to observe unfamiliar scenes) and motor functions (e.g., left-right differences in locomotion). There is a common tendency to assign observed structural or functional asymmetries to lateralization, which often involves more than a simple left-right difference in observed behavior. This narrative review explores the concept of laterality relative to the structural and functional asymmetries reported in horses. Inconsistent and poorly defined terminology, a widely disparate methodology, and a lack of standardized thresholds make it difficult to assess the presence or degree of laterality. Within this context, there seems to be limited evidence of laterality in horses and much more prevalent and stronger support for structural and functional asymmetries due to a wide range of well-established behavioral, nociceptive, and biomechanical mechanisms. The authors caution against generalizing the idea that all observed structural or functional asymmetries in horses are due to laterality.
Publication Date: 2025-01-21 PubMed ID: 39943060DOI: 10.3390/ani15030288Google Scholar: Lookup
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Summary
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The research article focuses on understanding the concept of laterality in horses and arguing the differences between laterality and asymmetry. The researchers reason that not all observed structural or functional differences in horses should be attributed to brain lateralization and they discuss the challenges with the assessment due to inconsistent terminology, differing methodologies, and lack of standard thresholds.
Understanding Laterality and Asymmetry
- The researchers discuss the concept of laterality, which is the dominance of one side of the brain controlling specific functions of paired organs or one side of the body.
- They also touch on the concepts of structural and functional asymmetries, which are common in horses and vary from anatomical features (like bone length) to sensory information (such as the use of one eye over the other to observe unfamiliar scenes), and motor functions (like left-right differences in motion).
- There is a tendency to associate observed structural or functional asymmetries with lateralization, which often involves more than a simple left-right difference.
Challenges in Assessing Laterality
- The researchers point out the challenges faced in defining and assessing laterality. These include inconsistent and loosely defined terminology, different methodologies being used, and a lack of standardized thresholds to determine the presence or degree of laterality.
- Such difficulties present obstacles in comparing studies and determining the extent of laterality.
Lateralization vs Asymmetry in Horses
- Contrary to popular belief, the researchers found that there was limited evidence of laterality in horses.
- On the other hand, they found stronger support for structural and functional asymmetries due to a wide range of established behavioral, nociceptive (pain perception), and biomechanical mechanisms.
- Therefore, they caution against automatically attributing observed structural and functional asymmetries in horses to lateralization, recommending further studies to distinctly separate the two concepts.
Cite This Article
APA
Haussler KK, le Jeune SS, MacKechnie-Guire R, Latif SN, Clayton HM.
(2025).
The Challenge of Defining Laterality in Horses: Is It Laterality or Just Asymmetry?
Animals (Basel), 15(3), 288.
https://doi.org/10.3390/ani15030288 Publication
Researcher Affiliations
- College of Veterinary Medicine, Lincoln Memorial University, Harrogate, TN 37752, USA.
- Department of Surgical and Radiological Sciences, University of California-Davis, Davis, CA 95616, USA.
- Equine Department, Hartpury University, Gloucester GL19 3BE, UK.
- Pferdepraxis Vetcheck GmbH, Wierezwil-Rüberi 273, 3255 Rapperswil BE, Bern, Switzerland.
- Large Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824, USA.
Grant Funding
- na / International Task Force on Laterality in Sport Horses
Citations
This article has been cited 2 times.- Gottleib K, Trager-Burns L, Santonastaso A, Bogers S, Werre S, Burns T, Byron C. Comparison of Gait Characteristics for Horses Without Shoes, with Steel Shoes, and with Aluminum Shoes. Animals (Basel) 2025 Aug 13;15(16).
- MacKechnie-Guire R, Clayton H, Byström A, Marlin D, Haussler K, Latif S, Blum N, le Jeune SS, Wanless M, Egenvall A. International Survey Exploring Rider-Perceived Sidedness of the Horse. Animals (Basel) 2025 Jul 2;15(13).
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