Phenotypic Characterisation of the Abruzzo Donkey (Equus asinus), an Endangered Italian Genetic Resource: Body Measurements.

The Abruzzo (AB) donkey is a mountain-adapted Italian population listed as a genetic resource at risk of extinction (census ≈ 600 animals; no studbook). We aimed to provide the first comprehensive morphometric description of the breed and to compare it with the Martina Franca (MF) donkey, its main progenitor. Sixty-nine adult donkeys (56 females, 13 males) from six farms were measured in 2024. Twenty-three linear traits plus body weight and body condition score were recorded three times by a single operator. Descriptive statistics, Welch's t-test or Mann-Whitney U test with Benjamini-Hochberg correction, PCA and LDA with leave-one-out cross-validation were performed in R; comparison with MF was based on published summary statistics. Coefficients of variation for the three studbook-admission parameters were ≤0.10 in both sexes. Sixteen of 26 traits showed significant sex dimorphism, with the largest effect sizes for rump height, medial canthal distance and wither height. LDA correctly classified 94% of animals by sex. AB females were significantly smaller than MF in 22 of 23 shared traits but had a wider thorax (p = 0.012). The sexual dimorphism observed in the Abruzzo donkey is male-biased and predominantly size-based, with a minor and well-localised shape component in the head region. Males are significantly larger than females for all axial measurements (wither height A: +6.5 cm, +5.3%; rump height B: +6.4 cm, +5.0%; trunk length D: +12.1 cm, +9.5%), for thoracic circumference (M: +7.1 cm, +5.0%), for body weight (+49.9 kg, +20.6%) and for the main head traits (CM: +4.3 cm, +20.0%; G: +3.6 cm, +12.5%; H: +1.3 cm, +11.1%; E: +2.0 cm, +3.8%); no trait shows a significant female bias after BH-FDR correction. The AB donkey shows a uniform mesomorphic phenotype, smaller and stockier than MF, supporting the establishment of an official studbook.