COMPARISONS OF SELENITE AND SELENIUM YEAST FEED SUPPLEMENTS ON SE-INCORPORATION, MASTITIS AND LEUKOCYTE FUNCTION IN SE-DEFICIENT DAIRY-COWS

The dairy cows at the Estonian Agricultural University appeared to hav e an extremely low selenium status. The selenium level was 5.6 mug/l i n whole blood and 3.2 mug/l in milk, on average. The blood glutathione peroxidase was consequently extremely low. The effects of organic sel enium (selenized yeast) and sodium selenite were compared in a feeding experiment on 100 dairy cows. Selenium incorporation, udder health an d the in vitro function of blood neutrophils were monitored. Supplemen tation of the feed either with 0.2 ppm organic selenium or sodium sele nite for 8 weeks, increased the blood selenium level (geometric mean) within this period from the background level (about 5.6 mug/l) to 167 (Se-yeast) and to 91 mug/l (selenite). The respective change in whole blood glutathione peroxidase (GSH-PX) was from 0.22 to 3.0 (Se-yeast) and to 2.3 (selenite) muKat/g Hb. Blood GSH-PX continued to increase u p to 10 weeks after the supplementation was stopped. The bioavailabili ty of yeast selenium was superior to selenite: the relative bioavailab ility (selenite = 1) of yeast selenium was 1.4 if blood GSH-PX, 1.9 if blood selenium, and 2.7 if milk selenium was used as the response cri terion. Selenium-supplementation showed a positive effect on udder hea lth. The percentage of quarters harbouring mastitis pathogens dropped from 22.9 to 13.0 in the Se-yeast group and from 18.4 to 7.4 in the se lenite group during the supplementation period. The effect of selenium on mastitis was also reflected as a decrease in the output of milk so matic cells and N-acetyl-beta-D-glucosaminidase (NAGase). The time-lum inescence profile of zymosan-induced activity of blood neutrophils bec ame skewed to the left in Se-supplemented cows.