Equine hoof size, shape and balance are products of complex natural conditions and man-made influences. Natural conditions include genetics and environment, while man-made influences are hoof trimming and shoes. Despite a long history of concern for its importance, proper hoof balance resulting from these factors remains difficult to evaluate and describe.
What’s Proper Balance?
Seven factors summarizing the complete description of hoof balance (Balch 1991) have been described as:
1. Toe length.
2. Hoof angle.
3. Mediolateral hoof orientation.
4. Sole, frog and bar thickness.
5. Wall contour and ground surface.
6. Pair symmetry of hooves and limbs.
7. Non-interference of hooves and limbs.
These seven factors incorporate three views of balance: static balance (geometric trimming to produce an axially symmetric hoof), dynamic balance (trimming for simultaneous landing of the heels) and result-oriented balance (trimming to minimize interference and lameness).
Each view has merit and the best application of trimming and shoeing techniques probably uses some of each.
Hoof balance has also been summarized as that hoof shape or conformation that best matches the physical and biomechanical characteristics of an individual horse so as to optimize performance and minimize the detrimental effects associated with the physical stress of locomotion. While this definition is very comprehensive, it is difficult to apply when trimming the hoof and has limited usefulness as an analytical tool.
Static hoof balance, on the other hand, is more easily applied clinically and measurements of it can be used for analytic research to better understand how hoof balance affects locomotion, lameness and injury.
There are countless methods for measuring static hoof balance, some dating back to the late 19th century (Dollar 1898). A few modern analytic studies have quantitatively measured selected aspects of static balance (such as toe angle and wall length) and used these measurements clinically (Turner 1989, Kobluk 1990, Snow and Birdsall 1991, Turner 1993).
However, the reliability of these techniques and how well they capture the variability between horses has not been reported. The technique described here offers a comprehensive, quantitative method for measuring equine hoof size, shape and static balance (geometric axial symmetry) using digital image analysis.
Materials And Methods
Front hooves were collected from over 100 horses presented to the California Veterinary Diagnostic Laboratory System for necropsy examination. Hooves were removed from the limbs above the coronary band, washed, dried, hair was clipped from the coronary band region and shoes were removed.
Each hoof was then attached to a 30 by 30-centimeter square board that fit into a holding jig, so right-angled digital images of the lateral, medial, dorsal and palmar sides of the hoof could be obtained by rotating the board in 90-degree increments.
After the hoof was removed from the holding jig, the circumference of the hoof wall at the ground surface, the corners of the heels and the bars were marked with chalk so these landmarks could be seen more easily on dark-colored hooves and a solar view was taken.
A video camera connected to a personal computer was used to obtain all images (Figure 1). A calibration ruler was included in each view and the focal distance for each image was 50 centimeters. Public domain image analysis software, NIH Image, was used to record calibrated angle, length and area measurements from each image. This software calculates angle, line segment length and area after tracing the structure of interest with a cursor (Figure 2).
Thirty-two hoof wall measurements were obtained from the lateral and medial (Figure 3), dorsal and palmar (Figure 4a and 4b) and solar views (Figure 5). Several additional measurements were calculated to assess axial symmetry (Transformations, Figures 3, 4 and 5 captions).
A coefficient was used as an index of reliability (repeatability with two observers each measuring the same image twice) when the technique was applied to 18 horses. This coefficient measures the proportion of variability in a set of measurements attributable to differences between horses as opposed to the effects of having two observers and random error.
Despite the widely recognized importance of proper hoof shape and balance, few techniques for comprehensive, quantitative measurement of equine hooves have been described in the scientific literature (Snow and Birdsall 1991, Turner 1993). The base of support measurements (including base of support difference) were developed using clinical insights reported in the literature (Moyer 1975, Moyer 1982) and were expected to reflect long-toe, low-heel balance problems.
X, Y, and Z length difference (Figure 3) and total wall length difference measurements were patterned after the measurement technique developed by Birdsall as reported by Snow and used clinically by Snow and Birdsall and Turner (Snow 1991, Snow and Birdsall 1991, Turner 1993). Several measurements using the point of the frog were based on an adaptation of Duckett’s theories and were expected to reflect mediolateral balance (Bumbaugh 1992).
Landmarks for most measurements were selected so comparable measurements might be taken from lateromedial radiographs of the hoof or from the hoof itself on live horses. Measurements described for the lateral view (with the exception of LWX, LWY and LWZ) have been successfully taken from lateromedial radiographs of the hoof. Most of the other measurements have been taken directly from the hooves themselves.
Specifically, the landmarks used for measurement of heel angle were chosen so that comparable measurements might be obtained from lateromedial radiographs. In retrospect, the angle of the most caudal horn tubules in the lateral view might have been a more accurate reflection of functional heel angle.
Ratios, proportions, measures of relative asymmetry (difference between A and B/mean of A and B) and standardization of measurements by body weight have all been used to adjust for size differences when comparing hoof measurements and limb conformation among horses (Kobluk 1990, Snow 1991, Linford 1993, Manning 1994). Similarly, hoof size, shape and balance could be measured relative to limb conformation as it is often viewed subjectively (Balch 1991).
Unfortunately, cadaver weight was not available for most study horses and could not be used to explore hoof measurements relative to body weight as described by Turner (1993). Due to the nature of the necropsy examinations performed on all the horses in the study, intact limbs were unavailable for measuring limb conformation.
Overall, intra- and inter-observer intraclass correlation coefficients (ICC) for hoof measurements were generally high (median values greater than 0.95 and 0.87, respectively) with little difference between observers and trials. Hoof measurements with physical landmarks (toe length) and imaginary landmarks (widest hoof width) had similar reliability (median values greater than 0.95); however, measurements of coronary band contour (LWX, LWY and LWZ) typically had lower reliability (median value less than 0.70).
Digital image analysis offers researchers a convenient method of getting difficult measurements from an irregularly shaped specimen (such as surface areas and angles) and preserves a record of each specimen for future use or review. The technique described here has good reliability for most measurements (Kane 1997) and was useful for an analytic evaluation of hoof measurements and injury (Kane 1998).
With some camera and positioning jig modifications, the technique described here could easily be used with live horses, and it is our hope that other researchers will find it useful.
1. A comprehensive, analytic approach to the evaluation of static hoof balance is possible.
2. Digital image analysis can be a reliable method of measuring static hoof balance, and with some modification similar measurements could be taken from lateromedial radiographs or directly from the hoof.
This research was conducted at the J.D. Wheat Veterinary Orthopedic Research Laboratory, School of Veterinary Medicine, University of California, Davis. The study was funded by the Grayson-Jockey Club Research Foundation, Inc.; the Center for Equine Health with funds provided by the Oak Tree Racing Association, the State of California satellite wagering fund, and contributions by private donors; Mr. and Mrs. Amory J. Cooke and the Hearst Foundation. This study resulted from the California Horse Racing Board Postmortem program.