Short communication: Vitamin D status and responses in dairy cows naturally infected with Mycobacterium avium ssp....

Serum samples were obtained from Holstein dairy control cows and cows naturally infected with Mycobacterium avium ssp. paratuberculosis (MAP) to evaluate the effects of disease status on serum 25-hydroxyvitamin D₃ (25OHD₃) levels. Disease status was stratified for infected cows into asymptomatic, subclinical infection (n = 25), and cows demonstrating clinical signs (n = 20), along with noninfected control (n = 12) cows for comparison. In addition, portions of the ileocecal valve were taken from a subsample of cows (n = 5 per treatment group) at necropsy and processed for RNA sequencing gene transcription studies. Genes associated with vitamin D metabolism were queried to determine any association between infection and gene expression. Serum 25OHD₃ levels were significantly lower in cows in the clinical stage of disease compared with either cows in the subclinical stage and noninfected control cows. Differential expression for genes associated with the vitamin D pathway such as CYP27A1, CYP27B1, vitamin D-binding protein (DBP), and IFNG was dependent upon infection status. An upregulation of CYP27A1 was noted for cows in subclinical status, whereas CYP27B1 expression was enhanced for clinical cows. Increased expression of vitamin D-binding protein was observed for infected cattle, regardless of infection status. In summary, decreases in circulating 25OHD₃ for animals with clinical disease may suggest that these cows have reduced innate immune responses, thereby influencing the ability of animals to fight infection.