Vertebral heart scale measurements in Asiatic black bears (Ursus thibetanus) and sun bears (Helarctos malayanus)

This retrospective study aimed to establish vertebral heart score (VHS) reference ranges for Asiatic black bear ( Ursus thibetanus ; ABB) and sun bear ( Helarctos malayanus ; SB), and to evaluate interspecific differences and the effects of biological variables on VHS measurement. Although cardiovascular disease is a common health concern for these species in captivity, objective radiographic reference ranges for cardiac size assessments are currently lacking. Thoracic radiographs from 46 clinically healthy sanctuary bears (22 ABBs, 24 SBs) were reviewed. VHS was measured on right lateral (RL) and dorsoventral (DV) views, and thoracic conformation was quantified using the thoracic depth-to-width (D/W) ratio. The influence of sex, age, and morphometric parameters (body weight, body condition score, and chest circumference) on VHS was evaluated within each species. In ABBs, the mean VHS was 10.65 ± 0.48 vertebrae (v) (95% range, 9.90 ‒ 11.67) on RL view and 10.82 ± 0.73 v (95% range, 8.90 ‒ 11.96) on DV views. Corresponding values in SBs were 10.68 ± 0.62 v (RL) (95% range, 9.19 ‒ 11.68) and 11.18 ± 0.67 v (DV) (95% range, 10.13 ‒ 12.28). No significant differences in VHS were observed between the two species, despite distinct differences in thoracic conformation; D/W ratio was 0.73‒1.00 (95% range) in ABBs and 0.59‒0.77 (95% range) in SBs. Sex, age, and morphometric variables were not significantly associated with VHS in either species. Despite significant interspecific variations in thoracic morphology, the VHS remained consistent between species and robust across various biological traits. These species-specific VHS reference ranges provide a practical radiographic tool for objective screening of cardiomegaly and longitudinal monitoring of cardiac size in captive bears, enhancing the clinical management and welfare of captive bears.