Comparison of Donkey, Pony, and Horse Dorsal Profiles and Head Shapes Using Geometric Morphometrics

SIMPLE SUMMARY: With the increasing interest toward donkey breeding and equid welfare, the scales and methods of welfare assessment, which were successfully designed and validated for horses, are a starting point for the development of similar approaches for donkeys. As horses and donkeys are morphometrically different, the current study aimed to compare donkey, pony, and horse dorsal profiles and head shapes. Geometric morphometrics (GM) was applied to characterize the shapes and sizes of the studied equids based on the analysis of the photographs of 14 donkeys, 14 ponies, and 14 horses. The donkeys differed from ponies and horses in the shape of the dorsal profile and the head shape, but only from horses in the size of the evaluated centroids. Moreover, the ponies and horses differed in size but not in the shape of the investigated lines reflecting the posture and head contour. When both lines were compared, the GM distances (the Mahalanobis and Procrustes distances) were higher between donkeys and ponies and horses than between ponies and horses. GM revealed the differences in dorsal profiles and head shapes between equids, which should be considered when adapting scales and methods of welfare assessment from horses to donkeys. ABSTRACT: Since donkey breeding has increased due to their variety of uses, welfare evaluation has become more important. This study aimed to compare donkey, pony, and horse dorsal profiles and head shapes using geometric morphometrics (GM). Photographs of 14 donkeys, 14 ponies, and 14 horses were analyzed using GM, including the sliding semilandmarks method. The variations in the first three principal components (PCs) were PC1: 57.16%, PC2: 16.05%, and PC3: 8.31% for the dorsal profiles and PC1: 44.77%, PC2: 13.46%, and PC3: 7.66% for the head shapes. Both the dorsal profiles and head shapes differed between donkeys and horses (p < 0.0001) but not between donkeys and ponies (p > 0.05). Moreover, both the dorsal profiles and head shapes differed in size between ponies and horses (p < 0.0001) but not in shape (p > 0.05). Higher Mahalanobis and Procrustes distances were noted between donkeys and horses as well between donkeys and ponies than between ponies and horses. The use of geometric morphometrics revealed the differences in the dorsal profiles and head shapes between the studied equids. These differences should be taken into account when adapting welfare scales and methods from horses to donkeys.