EFFECTS OF SUPPLEMENTAL CHROMIUM ON IMMUNE-RESPONSES OF PERIPARTURIENT AND EARLY LACTATION DAIRY-COWS

The objective of the present study was to determine the effects of supplemental dietary chromium on immune responses of dairy cows subjected to physical and metabolic stresses associated with late pregnancy, calving, early lactation, and peak milk yield. Nine periparturient dairy cows were supplemented with chelated Cr (.5 ppm/d) from 6 wk prepartum (wk -6) through 16 wk postpartum (wk 16), and 10 cows were unsupplemented controls. To assess humoral immune responses, all cows were immunized with ovalbumin (OVA; .c.) and human erythrocytes (HRBC; i.v.) on wk -2 and 2, and sera from weekly blood samples were assayed for content of antigen-specific antibody. Cell-mediated immunity was assessed in vitro using antigen (OVA)- and mitogen-stimulated peripheral blood mononuclear cell (PBMC) blastogenesis of cells collected biweekly from wk-2 and 6. Supplemental Cr caused anti-OVA antibody responses (P < .01) and mitogen-stimulated blastogenic responses of PBMC (P = .05) to be elevated, was associated with lowered OVA-stimulated blastogenic responses of PBMC (P < .01), and had no overall effect on antibody responses to HRBC (P > .10) relative to responses of control cows. These results confirmed and extended our previous observations that supplemental Cr can alter specific immune responses of stressed cattle.