IMMUNOMODULATORY ACTIVITY OF BLOOD-SERUM FROM CHROMIUM-SUPPLEMENTED PERIPARTURIENT DAIRY-COWS

Our previous research showed enhanced immune responses, including mito gen-induced blastogenesis of peripheral blood mononuclear cells from f eedlot calves and periparturient dairy cows supplemented with dietary chromium (Cr). The objectives of the present study were to test whethe r blood sera from Cr-supplemented periparturient cows contained immuno modulatory activity for mitogen-stimulated peripheral blood mononuclea r cells and, if so, to determine if this activity was explicable by di fferences in blood profiles of some glucose-regulating hormones (insul in, cortisol, growth hormone, insulin-like growth factor I, and tumor necrosis factor-ct) between Cr-supplemented and unsupplemented (contro l) animals. Blood sera from ten unsupplemented cows and nine Cr-supple mented cows (0.5 ppm day(-1)) were collected weekly from 2 weeks befor e to 6 weeks after parturition, and were used to supplement (1, 10, an d 20% vol/vol) culture medium supporting concanavalin A (Con A) stimul ated mononuclear cells enriched from blood of four nulliparous donor c ows. Hormone concentrations were determined using radioimmunoassays. C on A-induced blastogenesis was enhanced when 1, 10, and 20% sera from Cr-supplemented cows was added to the mononuclear cell cultures, and t his was particularly evident around parturition. Conversely, peripartu m sera from unsupplemented cows depressed Con A-induced blastogenesis. Except for a marginal rise in blood cortisol 2-4 weeks after parturit ion, no significant effects of Cr supplementation on other hormones (i nsulin, growth hormone, insulin-like growth factor I, tumor necrosis f actor-alpha) were observed. These observations suggest that factors in peripheral blood serum from Cr-supplemented cows, other than absolute concentrations of the glucose-regulating hormones studied, modulate C on A-induced blastogenesis of mononuclear leukocytes.