Milk selenium concentration and its association with udder health in Atlantic Canadian dairy herds

Soils and plants in Atlantic Canadian provinces are known to contain low concentrations of selenium (Se). Earlier studies have indicated that dairy producers in Atlantic Canada are providing insufficient supplementary Se in the ration to meet the Se requirements of dairy cattle, as measured by herd-level milk Se concentration. The objective of this study was to evaluate the association between milk Se concentration and somatic cell count (SCC) and the risk of new intramammary infection (IMI) in the dry period, in Atlantic Canadian dairy cows. Eighteen dairy farms participating in the Canadian Bovine Mastitis Research Network cohort study were selected as a convenience sample. On each farm 15 cows to be dried off were selected. Quarter milk samples were collected at 4 and 2 wk before drying-off, within 24 h after calving, and at 7 d after calving to evaluate IMI status. Composite milk samples were analyzed for SCC and Se concentration. Mean milk Se concentration was marginal in 14% of the cows that were on pasture during the grazing season. Milk Se concentration was not associated with the overall odds of new IMI in the dry period; however, the odds of having a new Streptococcus spp. and other gram-positive pathogen IMI in the dry period increased with increasing milk Se concentration. Somatic cell count increased with milk Se concentration, even after adjusting for IMI status. The dairy population in our study had higher ranges for milk Se concentration, whereas ranges for prevalence of IMI, and SCC were lower, compared with those in studies where a negative relationship between Se status and udder health was first noted. Therefore, under the current management conditions, milk Se concentration did not appear to be a principal determinant of udder health.