Retrospective studbook analysis of morphometric structure, body indices, and coat color distribution in Pêga donkeys

Phenotypic characterization of populations allows the description of morphometric variation, body proportionality, and breed qualification documented in official registry systems.

This study characterized morphometric structure, body indices, and temporal coat color distribution in Pêga donkeys.

This retrospective studbook study used 46,517 unique Pêga donkey records from 1901-2020. Analysis-specific subsets included 9,093 animals for PCA and coat color, 4,635 for factorial ANOVA, and 1,477 for body indices. ANOVA sensitivity was evaluated with HC3 covariance estimates, PCA retention with 1,000-iteration parallel analysis, and coat color trends with multinomial regression and generalized additive models.

The conventional and HC3 analyses agreed for all 45 trait-by-effect tests. Sex affected 14 of 15 measurements, age class affected 12, and two age × sex interactions were detected. Age and interaction effects were small (maximum partial η² = 0.011 and 0.003, respectively), whereas the largest sex effect was observed for chest width (partial η² = 0.167). Parallel analysis confirmed the three PCA components retained by the Kaiser criterion; together they explained 57.7% of variance. Body indices described a more elongated conformation in recent males, but these indirect classifications do not demonstrate performance or an aptitude change. Coat color composition varied with birth year (likelihood-ratio χ² = 374.50, df = 6, p < 0.001).

The historical registry provides a large phenotypic reference for Pêga donkeys. Temporal differences should be interpreted as changes among recorded birth cohorts and registry categories, rather than direct evidence of performance, causal selection, or population-wide change.