Background We aimed to identify a simple test for excessive calciuresis and predict calcium oxalate (CaOx) disease in Miniature Schnauzers. We investigated the impact of postprandial time on the urine calcium to creatinine ratio (UCa/Cr) in male dogs of this breed, with the goal of improving the utility of the UCa/Cr. Hypotheses (1) Significant differences will exist in preprandial and postprandial UCa/Cr between CaOx urolith-forming and control Schnauzers. (2) The UCa/Cr will increase significantly from the first morning baseline at >= 1 postprandial time point(s) in both control and CaOx urolith-forming dogs. (3) Biochemical abnormalities and other variables may be associated with urolith status. Animals Twenty-four male Miniature Schnauzer dogs, consisting of 9 with (urolith formers) and 15 without (controls) CaOx uroliths. Methods Urine was collected before and 1, 2, 4, and 8 hours after feeding a standardized diet. Receiver operator characteristic curve analysis was performed to identify the UCa/Cr cutoff that most accurately differentiates dogs based on urolith status. Results Urolith formers had significantly higher mean UCa/Cr over the course of 8 hours. The postprandial change in UCa/Cr was not significant at any time point between or within groups. The cutoff UCa/Cr value of 0.06 had a specificity of 93% (95% confidence interval [CI], 80%-100%) and a sensitivity of 56% (95% CI, 21%-86%) for identifying CaOx urolithiasis. Conclusions and Clinical Importance Urolith-forming male Miniature Schnauzers have excessive calciuresis, and the postprandial sampling time up to 8 hours is not critical. This simple urine measurement has potential as a marker of CaOx disease.