Cranial Shape Variation in Adult Kyrgyz Horses: Associations with Size and Sex

Cranial diversity within indigenous horse populations remains incompletely characterized. Cranial shape variation and its associations with skull size and sex were investigated in 37 adult Kyrgyz horses aged 4–5 years (18 females and 19 males). Three-dimensional configurations of 25 cranial landmarks were evaluated using Procrustes alignment, principal component analysis, and permutation-based multivariate models. Skull size was quantified using centroid size calculated from the landmark configurations. The first two principal components represented 29.41% of shape variance, with changes distributed across multiple cranial regions and substantial overlap between sexes. A 5.42% greater mean centroid size was observed in males (p < 0.001). In separate models, 5.17% and 4.92% of shape variance were explained by sex and allometry, respectively (both p < 0.05). After size adjustment, neither an additional sex effect nor a size-by-sex interaction was statistically supported (both p > 0.05). Small, localized differences were observed between adjusted mean configurations. Cranial variation was therefore characterized by changes across several anatomical regions, a modest association with size, and limited evidence for additional sexual shape differentiation after size adjustment.