Vitamin D supplementation in dogs with chronic biliary tract diseases.

Extrahepatic cholestasis in dogs is frequently associated with reduced intestinal absorption of fat-soluble vitamins, resulting in suboptimal vitamin D status. This prospective longitudinal study assessed the effects of six-week oral cholecalciferol supplementation (40 IU/kg/day) on serum 25-hydroxycholecalciferol [25(OH)D] in fourteen dogs with chronic biliary disease. Median baseline 25(OH)D concentration was 2.3ng/mL (0.3-11.2), increasing to 4.3ng/mL (2.4-14.0) after treatment, whereas healthy controls (n = 31) showed 11.68ng/mL (2.65-37.93). Statistical analyses (paired Wilcoxon tests) confirmed a significant increase post-supplementation (p = 0.003). Ionized calcium and phosphorus levels were stable, and no hypercalcemia occurred. Biochemical parameters (alkaline phosphatase, alanine aminotransferase, gamma-glutamyl transferase, cholesterol, total bilirubin) showed nonsignificant downward trends, indicating good hepatic tolerance. Cholecalciferol supplementation was thus safe and effectively improved vitamin D status, although concentrations remained lower than those observed in the study's healthy controls. The heterogeneous response suggests variable intestinal absorption or disease severity. Further controlled, long-term studies are needed to refine dosing strategies and clarify potential hepatic and clinical benefits.