Biometric Evaluation Using Body Measurements of Jiangyue Donkeys

Body measurements provide a non-invasive basis for estimating live weight, yet their predictive value and age-related variation remain poorly characterized in female Jiangyue donkeys. Body weight (BW) and 11 morphometric traits were recorded in 484 females: withers height (WH), body length (BL), chest circumference (CC), cannon circumference (CAC), head length (HL), neck length (NL), chest width (CW), chest depth (CD), rump height (RH), rump length (RL), and rump width (RW). Descriptive statistics, correlation analyses, and regression analyses were performed using SPSS 27.0; stepwise regression was then applied to derive and validate BW prediction equations. Additionally, four nonlinear functions—Logistic, Gompertz, Brody, and von Bertalanffy—were fitted to cross-sectional BW data from 241 females sampled at different ages to characterize the population-level relationship between age and weight. BW was positively correlated with all morphometric traits (p < 0.01), with CC showing the strongest association. The optimal equations explained 91.8% and 84.4% of the variation in BW among growing and adult donkeys, respectively (both p < 0.01). Of the four nonlinear functions evaluated, the Brody model provided the closest fit (R2 = 0.99960) and yielded an estimated asymptotic mature weight of 191.049 kg. Because the age–weight analysis was based on cross-sectional observations, the resulting curve represents population-level variation rather than within-animal growth trajectories. Collectively, these models offer quantitative tools for live-weight estimation, growth assessment, and herd management in female Jiangyue donkeys.