CRP and diabetes mellitus: This prospective case–control study had three objectives (i) to compare granulocyte/monocyte (GM) phagocytic capacity of Escherichia coli (E. coli), concentrations of serum vitamin D metabolites, CRP, and basal plasma cytokines in diabetic dogs and non-diabetic healthy controls, (ii) assess whether clinical control of diabetes mellitus affects these variables, and (iii) evaluate whether associations exist between vitamin D metabolites and inflammatory biomarkers or phagocytic capacity.