Comparison of American Quarter Horses Competing in Western Pleasure, Hunter under Saddle, and Reining Using Linear Traits.

To investigate differences in American Quarter Horses conformation suggesting specialization and subpopulations within the breed, a total of 45 horses were studied. These horses were classified according to their specific sport discipline: Western Pleasure (WPL, n = 15), Hunter under Saddle (HUS, n = 15), and Reining (RN, n = 15). Fifteen linear traits (comprising lengths, angles, and circumferences) were measured analogically and photometrically. Afterwards, 9 ratios and differences were calculated, so that a total of 24 traits were examined. The results showed significant differences between horses depending on their sport discipline. HUS horses were significant taller and were characterized by higher values in (nearly) all length traits; they were followed by WPL and RN horses. RN horses displayed the lowest values in length traits but the largest difference between height at withers and height at croup. Nine parameters were analyzed through correlations to the height at withers; all differences were significant, with high to moderate correlation coefficients. The detected differences between the groups support recent studies on the conformation and genotype of subpopulations within a breed and reveal new findings in relation to the selected disciplines. Image analysis worked well and provided reliable data; therefore, this method can be used to examine horses in a time-efficient manner, reducing the stress caused to the animal. Further studies are required to gain more information and to associate the features of AQH anatomic structures with successful performance.