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Use of an Equine Back Profiling System for Objectively Measuring Trunk Contours

Take Home Message

Current saddle fitting methods do not provide a quantifiable or standardized method for assessing three-dimensional trunk morphometry. The Equine Back Profiling System (EBPS) was able to reliably capture a wide variety of dorsal trunk contours of horses ridden under English dressage or jumping saddles as well as Western saddles. The EBPS provides a significant advancement as we are now be able to better communicate findings or changes in dorsal trunk contours related to saddle fit to colleagues or owners and trainers.

Introduction

The goal of saddle makers and fitters is to match the size and shape of a specific saddle as closely as possible to an individual horse's dorsal trunk contour in an effort to maximize surface area and to provide uniform, low-pressure distribution patterns without limiting performance.1 However, current saddle fitting methods do not provide a quantifiable or standardized method to assess three-dimensional morphometry, which means that saddle manufacturers are unable to produce a consistent product that is able match the wide variability present in different body types and trunk morphologies. Even after centuries of applying saddles to ridden horses, there is no established industry-wide standard for assessing the size or shape of a horse's trunk in an effort to improve saddle fit and reduce associated back pain.2 Unfortunately, the majority of descriptions of equine trunk shape and size are nondescript and not clinically useful.3 Morphometric features (i.e., height, length, depth, and width) of a horse's trunk can provide objective measures of body size or shape that are required to quantify specific segmental characteristics or general body conformations.4,5 However, it continues to be difficult to capture and quantify surface contours, which are considered critically important for establishing uniformity between the contours of the ventral surface of the saddle and the dorsal surface of the trunk of the horse.6,7
 
The EBPS consists of a series of durable plastic cards with cut-out contours that are positioned at several predetermined anatomical sites along the dorsal trunk in an effort to provide an objective assessment of conformation and contours relevant to proper saddle construction and fitting. The cards are reportedly easy to use and provide a potential method for quantifying the dorsal trunk morphology across a wide-variety of body types and breeds of horses. The EBPS may provide a standardized method to quantify the shape of a horse's trunk, which would be a significant advancement in improving saddle construction, standardizing saddle fit, and reducing the prevalence of trunk pain in ridden horses. The objective of this study was to assess the ability of the EBPS to readily quantify the contours of the dorsal trunk in several breeds of horses used in different athletic disciplines.
 
This project was completed by Drs. Kevin Haussler, Ashley Hill, Wayne McIlwraith, and Chris Kawcak with Sierra L. Blauvelt and Jodi Callison at Colorado State University.

Methods

Each EBPS transverse card contained three or four cut-out contours that were able to capture a total of 33 different transverse contours of the dorsal trunk (Figure 1). The cards were placed transversely at six specified dorsal trunk locations that included the following sites: 1) widest portion of the withers, 2) highest point of the withers, 3) caudal edge of the scapula, 4) base of the withers (i.e., where the slope of the withers transitions into a more horizontal curvature of the trunk), 5) lowest point of the trunk, and 6) the thoracolumbar junction (Figure 2). These six vertebral locations were judged to be the minimum number of sites needed to optimally capture potential variations in the dorsal trunk contours across different breeds of horses using both English and Western saddles.
 
The EBPS also contains two cards used to capture the parasagittal contours of the dorsal trunk in the region of typical Western saddle tree bar or English panel placement (Figure 3). The parasagittal cards were positioned 10-cm lateral to the dorsal midline of the trunk over the left and right epaxial musculature to assess bilateral longitudinal contours. Chi-squared analysis was used for nominal (unordered) data and Spearman Rank correlations was used for ordered and continuous data comparisons. Kruskal-Wallis one-way analysis of variance was used if one variable consisted of continuous data and post-hoc analysis was done using Bonferroni adjustment.

Results

The EBPS readily quantified the dorsal trunk contours in these horses. The transverse contours at the widest point of the withers were mostly narrow and 35% (n=73) of cards were judged to have good fit (< 0.5 cm). At the highest point of the withers, 39% (n=82) of transverse cards had a good fit. The widest and highest points of the withers were located at the same site in 64% (n=135) of horses. At the caudal aspect of the scapula, 89% (n=188) of transverse cards had a good fit and only 4% of regions had a gap height > 0.5 cm. At the base of the withers, 77% (n=163) of cards had a good fit and 5% of regions had a gap height > 0.5 cm. At the lowest point of the trunk, 97% (n=205) of cards had a good fit and 1% of regions within a card had a gap height > 0.5 cm. At the thoracolumbar junction, 91% (n=191) of cards had a good fit and 2% of regions within a card had a gap height > 0.5 cm. The transverse contour measurements at the three cranial vertebral locations (i.e., widest, highest and caudal scapula sites) were not significantly different from each other; however, the caudal three vertebral locations (i.e., base, lowest and thoracolumbar sites) were all significantly different from the cranial vertebral locations and each other.
 
Over the left epaxial musculature, 89% (n=187) of parasagittal cards had a good fit and 2% of quadrants had a gap height > 0.5 cm. Over the right epaxial musculature, 92% (n=195) of cards had a good fit and 2% of quadrants had gap heights > 0.5 cm. There were significant associations between the parasagittal card sizes and breed and athletic discipline. Warmbloods had flatter longitudinal contours and Morgans had more epaxial muscle concavity. For use, hunter-jumpers had the least amount of longitudinal epaxial muscle concavity and Morgans had the most muscular concavity.

Discussion

The objective of this study was to assess the ability of the EBPS to readily quantify the contours of the dorsal trunk in several breeds of horses used in different athletic disciplines. Using the three transverse locations and the left parasagittal site recommended by the EBPS manufacturer, the overall success rate was 92% as defined by overall gap heights < 0.5 cm within a card. The parasagittal cards had similar high rate of success (89-92%) as did the transverse cards at the manufacturer's recommended sites for measuring dorsal trunk contours. Across all four recommended vertebral locations, there was a 72% percent chance that all four cards had a good fit with gap heights < 0.5 cm within an individual horse. The EBPS was easy to use and was able to quantitatively capture subtle differences in trunk contours across horses of significantly different ages, wither heights, body weights, breeds, and uses of horses judged to have diverse trunk conformations. This suggests that the EBPS can be used to reliability capture the dorsal trunk contours in horses in an effort to improve saddle fit and construction in ridden horses.

Acknowledgement

Supported in part (or total) by the PVM student grant program in the Center for Companion Animal Studies at Colorado State University.

References

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  3. Harman J. Confounding variables: fitting saddles to every horse. In: Harman J., ed. The horse's pain-free back and saddle-fit book: ensure soundness and comfort with back analysts and correct use of saddles and pads. North Pomfret, Vt.: Trafalgar Square Publishing; 2004;113-134.
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  5. Bennet D. Conformation insights: Back shape & saddle fit. Equus 2010;April:59-67.
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  9. Brooks S.A., Makvandi-Nejad S., Chu E., et al. Morphological variation in the horse: defining complex traits of body size and shape. Anim Genet 2010;41 Suppl 2:159-165.
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  13. Fruehwirth B., Peham C., Scheidl M., et al. Evaluation of pressure distribution under an English saddle at walk, trot and canter. Equine Vet J 2004;36:754-757.
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