Dr Jennifer Irwin

The immunomodulatory potential of dietary chromium (Cr) has been demonstrated in cattle. Specific Cr-attributed health and production benefits, in both beef and dairy cattle, are postulated to arise in part from the direct and/or indirect consequences of this immunomodulatory potential and from the long-recognized effects of Cr on insulin and glucose metabolism. Recent studies in dairy heifers evaluated: (1) peripheral tissue responsiveness to insulin following feed supplementation with varying concentrations of Cr-yeast, and (2) blood lymphocyte (BL) insulin receptor expression and binding affinity following dietary supplementation with Cr-chelate. These findings suggest that Cr potentiation of insulin action may be mediated primarily by postreceptor pathways. In addition, in vitro studies examined the effect of Cr-supplemented culture medium on the quantitative expression of several cytokine mRNAs in concanavalin A (ConA)-stimulated bovine BLs. These findings support a previously reported Cr-mediated decrease in interleukin-2 (IL-2) activity in the culture medium of ConA-stimulated BLs from Cr-supplemented cows. They further suggest a role for immunoregulatory cytokines, particularly IL-2, as a mechanism through which Cr exerts its effects upon the bovine immune response. Additionally, the differential inhibition of bacterial growth rates by Cr in vitro, simulating possible effects upon anaerobic rumen bacteria populations, suggests a potential indirect mechanism by which dietary Cr may influence ruminant health and performance. The next generation of studies elucidating the cellular and molecular mechanism of Cr immunomodulatory effects will benefit greatly from a reliable, chemically defined source of Cr bioplexes and from the experience with Cr in ruminants.