Reduced levels of serum 25(OH)D3 are associated with tuberculosis positive cattle under conditions of high natural exposure to Mycobacterium bovis.

Serum vitamin D (25(OH)D3) concentrations of < 30 ng/mL in cattle are insufficient to induce an adequate immune response against intracellular pathogens, which suggests that the efficacy of the immune response may be highly dependent on the bioavailability of 25(OH)D3. This study shows an overview of both in vitro and in vivo 25(OH)D3-mediated immune modulation amongst dairy cattle naturally exposed to M. bovis. Tuberculin status was confirmed by interferon gamma release assay (IGRA), and natural exposure was demonstrated by polymerase chain reaction (PCR). Tuberculin (-) cattle have a higher serum concentration of 25(OH)D3 (X¯= 87.12 ng/mL) when compared to tuberculin (+) cattle (X¯ = 45.86 ng/mL). Reduced serum 25(OH)D3 levels are associated with the presence of bovine TB, and serum 25(OH)D3 levels of > 80 ng/mL are necessary to counteract infection by M. bovis. Kill assays were performed to evaluate in vitro 25(OH)D3 modulation of intracellular M. bovis growth in bovine macrophages, which showed that reduced serum 25(OH)D3 levels are associated with diminished mycobactericidal capacity in this experimental model. On the other hand, increased 25(OH)D3 in culture media enhances phagocytosis and nitric oxide production, which in turn improves capacity to combat M. bovis.