Background: Biliary sludge is associated with gallbladder (GB) dysmotility and mucus hypersecretion suggesting a link between biliary sludge, and the formation of GB mucoceles (GMT). If biliary sludge progresses to GBM, treatment to reduce the production and progression of sludge is warranted. Hypothesis/Objectives: The objective of this study was to determine the course of biliary sludge in dogs. Animals: Seventy-seven healthy, client-owned dogs >= 4 years of age screened for biliary sludge; 45 affected dogs identified. Methods: Prospective, observational design. Serial ultrasound examinations were evaluated at 3, 6, 9, and 12 months to monitor degree of sludge based on proportion of GB filled with sludge (mild [0.01-24.4%] moderate [24.5-49.4%] moderate to severe [49.5-74.4%] severe, [74.5-100%), gravity dependency of sludge, and GB dimensions.

Results: Alter 1 year of follow-up, the degree of sludge was mild (34 %), moderate (47% moderate to severe. (13%), severe (30 or absent (3%). There was no significant difference in median degree of sludge over 1 year (P = .36). There were no significant changes in the gravity dependency of sludge over 1 year. A subset of dogs, 24 %, with initial gravity-dependent sludge developed a combination of nondependent and dependent sludge. Dogs had resolved (2%), decreased (19%), static (40%), increased (29%), or recurrent (10 %) sludge at the conclusion of the study. Conclusions and Clinical Importance: Biliary sludge was prevalent, affected dogs remained asymptomatic, and it rarely resolves in healthy dogs over a period of 1 year. Some dogs developed nongravity-dependent sludge within 1 year, which might indicate changes in consistency of sludge.