Abstract

"The effect of selenium (Se) supplementation on the immune response to tetanus toxoid and Brucella abortus strain RB51 vaccines was studied in heifers with a normal Se status (GSH-Px activity > 130 U/g Hb). Frisian heifers (n-32), 18 to 24 months old were randomly allocated into two groups of 16 animals each. Animals from one group were supplemented (Se-S) with one dose of barium selenate (1 mg/Se/kg. s.c.) on day 0; animals from the other group remained as a control without supplementation (No-S). The heifers grazed during 9 months (April to January) a pasture that contained 0.04 ppm/DM of Se. All animals were vaccinated with Brucella abortus strain RB51 (day 60) and tetanus toxoid (days 120 and 150). Blood samples were obtained before supplementation and each 15 days until the end of the experiment. The Se status was assessed by determination of the blood GSH-Px activity. The specific antibodies to antigens were determined by ELISA technique and the cellular inmune response to Brucella abortus antigen was determined by intradermic reaction test. Selenium administration produced an increase (P < 0,05) in blood GSH-Px activity to between 339 and 579 U/g Hb during the immune response experimental period. Selenium administration did not affect the humoral immune response to RB51 vaccine and tetanus toxoid (P > 0,05). However, the cellular inmune response to RB51 in Se-S heifers was decreased (P < 0,05). It is concluded that Se supplementation in heifers with a normal Se status kept under farm conditions does not affect the humoral immune response to RB51 vaccine and tetanus toxoid, but reduces the cellular immune response to RB51 vaccine"