Mechanical loading is considered to be one of several stimuli that cause changes in the shape and morphology of equine hooves; however, supporting evidence for any response to this form of stress is circumstantial. The nature of such responses has not been characterized, and it is unknown whether these responses are adaptive (ie, appropriate to the stimulus). Elucidation of the role of hooves in modulating interactions between a horse and a substrate is crucial for understanding hoof biomechanics and preventing mechanically induced lameness. It has been estimated that > 30% of lameness issues in horses are associated with foot problems.1 Therefore, knowledge of the responses of hooves to mechanical stress is relevant to issues of health and welfare for horses. Failure of individual bones and soft tissues of the musculoskeletal system and lameness are major concerns of the equine industry from the perspectives of health and welfare of horses and of economic losses (ie, treatment costs and days lost for racing and training).
A concern for all sport horse disciplines (eg, racing, show jumping, dressage, and endurance riding) is conditioning the musculoskeletal system to support the loads imposed during strenuous exercise. Limbs of equids can adapt to imposed stresses. The third metacarpal bones and associated tendons and ligaments in horses were the focus of previous studies2–5; however, to our knowledge, the responses of hooves to exercise have not been evaluated. The distal phalanx acts as a stable platform, and its morphometric response to exercise is minimal.6 Differences in anatomic characteristics of the primary epidermal laminae in response to exercise have been detected and were attributed to responses to variation in the loads applied to the hooves.7,a
The hoof wall is relatively hard and insensitive and acts as a barrier to protect the structures within the hoof capsule. The shapes of the hoof capsule and the inner structures affect how forces generated during hoof contact with the ground are transmitted through the capsule to the skeleton (ie, distribution of stress in the capsule and deeper structures is partly dependent on hoof shape). Some variables of capsule shape and internal anatomic characteristics of hooves (ie, laminar morphology) are correlated.7,a Our group recently reported7 a correlation between laminar morphology and capsule shape and also detected different patterns of correlation for anatomic variables between Standardbreds and Thoroughbreds; this difference could be related to different gaits and exercise patterns between these 2 breeds.
The repeated loading that is imposed over time during activities such as regular exercise causes changes in the magnitude of the applied stress. Additionally, changes in distribution of stress may be induced. Such loading may stimulate biologic responses that alter hoof morphology. Changes in the mechanical behavior of hooves in response to alterations in loading or extrinsic or intrinsic modifiers develop over time.a There is empirical evidence that exercise influences hoof morphology and biomechanics in horses, but this has not been evaluated experimentally to our knowledge. Evaluation of potential relationships over time among capsule thickness (hoof wall thickness and dermis thickness), capsule shape (hoof shape), and growth of the hoof wall requires assessment of variables associated with these characteristics in live horses and at the same time points. The purpose of the study reported here was to evaluate the influence of mild exercise over time on growth of the hoof wall and hoof morphology in Standardbreds.
Magnetic resonance imaging
Faramarzi B. Morphology of the equine laminar junction correlated with external anatomy of the hoof. MSc thesis, Department of Biomedical Sciences, University of Guelph, Guelph, ON, Canada, 2003.
Panasonic VDR-M30 digital camera, Panasonic Consumer Electronics Co, Elgin, Ill.
Optimas 6.5 image analysis software, BioScan Inc, Edmonds, Wash.
1.5 Tesla whole-body scanner, General Electric Healthcare, Milwaukee, Wis.
Volume Viewer Software, GE Advantage Windows Workstation Software 4.2, General Electric Healthcare, Milwaukee, Wis.
Proc Mixed, SAS, version 9.1.3, SAS Institute Inc, Cary, NC.
Proc Univariate, SAS, version 9.1.3, SAS Institute Inc, Cary, NC.
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