Morphometric and Histological Characterization of Chestnuts in Dezhou Donkeys and Associations with Phenotypic Traits.

Background: Chestnuts are keratinized skin structures found on equine limbs, but their characteristics in donkeys remain poorly understood. This study aimed to characterize chestnut morphology and histology in Dezhou donkeys and examine correlations with phenotypic traits.

Methods: A cross-sectional study was conducted on 347 Dezhou donkeys (0.3-15 years, 79-419 kg). Chestnut dimensions were measured using precision calipers, and correlations were analyzed with age, body weight, limb measurements, and thoracolumbar vertebral counts. Histological analysis compared chestnut tissue with adjacent normal skin using standard H&E staining protocols.

Results: Donkeys exclusively possessed chestnuts on forelimbs, predominantly showing regular geometric configurations. Histologically, chestnut tissue exhibited marked hyperkeratosis (>30 cellular layers vs. 4-6 in normal skin), widespread melanocyte distribution throughout the epidermis, and complete absence of cutaneous appendages. In group A, strong positive correlations were observed between chestnut width and age (r = +0.527, p < 0.01), body weight (r = +0.538, p < 0.01), and limb measurements (r > +0.589 p < 0.01). No significant correlations existed with vertebral numbers. In group B Dezhou donkeys older than 2 years, the length and width of the forelimb chestnuts showed the strongest significant correlation with right forelimb measurements, while no significant correlations were observed with other variables (age, body weight, and hindlimb measurements).

Conclusions: Chestnuts in Dezhou donkeys represent specialized integumentary structures with unique histological features and strong correlations with somatic development. These findings support their potential utility as biometric markers for individual identification and indicate coordinated developmental regulation with overall growth patterns.