Comparison of Transverse Thoracolumbar Angles in Dressage and Endurance Horses Using 3D Light Scanning and Comparison with Commercial Saddle Gullet Angles

The thoracolumbar profile is of interest in relation to saddle design and saddle fit. Flexible-curve rulers have previously been used to gather thoracolumbar profiles in horses; however, 3D light scanning offers a potential non-contact alternative method to estimate the cross-sectional shape of the region in greater detail. The aims of this study were to (1) describe the thoracolumbar profiles of endurance and dressage horses using 3D light scanning and (2) compare the wither profiles to saddle manufacturers' gullet bar angles. 3D light scans of the thoracolumbar region were obtained from 23 fit and competing Arabian endurance horses and 21 dressage horses of mixed breed competing at advanced or higher, each from two different stables. Markers were placed by palpation on the caudal scapula (V1) and T18 (V4). Images were imported into Meshmixer. A transversely oriented plane cut was taken at the level of the marker of the left caudal scapula, perpendicular to the back surface (V1), and at the level of the marker at T18. Two further cuts were made at the base of the withers (V2) and the lowest point/midpoint of the back (V3). The mean transverse back angle at V1 was 87 ± 8° for the endurance horse sample and 99 ± 10° for the dressage horse sample (P < 0.0001), and at V4 was 141 ± 7° (endurance) and 144 ± 6° (dressage) (P < 0.0001). For both endurance horses and dressage horses, there was a significant effect of location on back transverse angle (V1 to V4; P < 0.001), with V1 the narrowest and V4 the widest. While there is little consistency in what gullet angle a "medium" gullet bar would actually be, the range of angles measured at the shoulder in the present study reflects the most common gullet sizes offered by six manufacturers of English saddles.