Supplementing the feed of
selenium-deficient diary cows with
selenium (Se)-yeast or
selenite at a level of 0.2 p.p.m. induced self-cure of subclinical
mastitis; the prevalence of quarters harbouring subclinical
mastitis (bacteriological criteria) decreased to about one half during the 8 week supplementation period. Three phenomena became apparent to explain the beneficial effect of
selenium on
mastitis: 1. The recruitment of phagocytes to the infected milk compartment of the udder was improved due to Se-supplementation; the correlation between
infection and the respective inflammatory response, as indicated by the somatic cell count (SCC) and the
N-acetyl-beta-D-glucosaminidase activity (
NAGase) of milk, was poor in
selenium-deficient cows.
Selenium supplementation significantly improved the correlation; 2.
Selenium supplementation induced an unspecified antibacterial activity in milk
lactoserum (whey), restricting in vitro growth of the
mastitis pathogens Escherichia coli, Staphylococcus aureus, Streptococcus agalactiae and Streptococcus uberis, bacterial growth rates in whey samples became inversely correlated with the respective blood
glutathione peroxidase activities (GSH-Px); and 3.
Selenium supplementation had an effect on redox activities and sulfhydryl activities in whey. These changes were correlated with in vitro bacterial growth rates.