Effects of oral selenium supplementation on mastitis markers and pathogens in Estonian cows.

The effects of selenium supplementation on mastitis parameters in milk and on glutathione peroxidase (GPx) levels in blood were evaluated. Fifty-five Estonian dairy cows were allocated to selenium-supplemented (n=39) and nonsupplemented (n=16) groups. The supplemented group received 0.2 ppm organic selenium in the form of selenium yeast in their diet daily for 8 weeks. The nonsupplemented cows received their standard diet with no selenium supplementation. Mastitis parameters (i.e., bacteriologic findings and somatic cell count, N-acetyl-beta-D-glucosaminidase, and bovine serum albumin concentration) and GPx levels were monitored. The increase in the activity of GPx was significantly (P<.001) greater in selenium-supplemented cows than in nonsupplemented ones. Milk samples from each quarter were examined before and 8 weeks after initiation of the study. The proportion of quarters still pathogen-free after 8 weeks was significantly (P<.01; odds ratio [OR]=9.7) higher in selenium-supplemented cows than in nonsupplemented cows. However, when quarters milk-tested as pathogen-infected at the start of the study were reexamined after 8 weeks, there was no significant (P=.14; OR 3.6) difference in the proportion of pathogen-free quarters between selenium-supplemented cows and nonsupplemented cows. Differential positive rate (Youden's index) revealed that individual quarters were more prone to be infected by pathogens when the blood GPx activities in cows were below the cutoff value of 3.3 microkat/g hemoglobin than when GPx activity was above this value. It was concluded that selenium supplementation in cows with low GPx activity seems to support udder defense mechanisms that favor reduction of the incidence of new mastitis cases.