Blood selenium concentrations and glutathione peroxidase activities in dairy herds with high and low somatic cell counts.

Two groups of dairy herds (16 herds/group) were studied to determine the relationship between the prevalence of mastitis in a herd and mean herd blood concentrations of vitamins A and E, beta-carotene, and selenium (Se). One group had a Dairy Herd Improvement Association 12-month mean herd somatic cell count (SCC) of less than or equal to 150,000 cells/ml. The second group had a Dairy Herd Improvement Association 12-month mean herd SCC of greater than or equal to 700,000 cells/ml. Once for each herd, duplicate milk samples were collected from each quarter of the lactating cows, and blood samples were collected from 21 cows in various stages of lactation. Serum concentrations of vitamin A, beta-carotene, and vitamin E and whole blood concentrations of Se and Se-dependent glutathione-peroxidase (GSH-Px) were determined. Significant differences between the 2 groups were not found with respect to serum concentrations of vitamin A, vitamin E, or beta-carotene. However, the herds with the low SCC (less than or equal to 150,000 cells/ml) had significantly higher mean (+/- SEM) blood GSH-Px activity (35.6 +/- 2.95 mU/mg of hemoglobin) than did the herds with the high SCC (20.2 +/- 2.38 mU/mg of Hb). Whole blood concentrations of Se also were significantly higher in the herds with low SCC (0.133 +/- 0.010 microgram/ml of blood) than in the herds with high SCC (0.074 +/- 0.007 microgram/ml of blood). Significant negative correlations were found between the prevalence of intramammary infection with major pathogens and mean herd activity of GSH-Px (r = -0.62) and mean herd concentrations of Se (r = -0.66).