Effects of chromium on health status, blood neutrophil phagocytosis and in vitro lymphocyte blastogenesis of dairy cows.

The objective of this study was to determine the effects of supplemental dietary chromium (Cr) on health status and mastitis-related parameters, as well as neutrophil phagocytic activity of dairy cows during late pregnancy and early lactation. In addition, possible interactions and involvements of Cr with insulin, cortisol, somatotropin (rBST) and insulin-like growth factor-1 (IGF-1) were directly investigated in vitro based on blastogenic responses using peripheral blood lymphocytes (PBL) of eight cows fed the control diet. Forty pregnant Holsteins, 18 primiparous and 22 multiparous, at week (wk) 6 before the expected calving dates were randomly assigned to treatments: control and supplemental chelated Cr (0.5 ppm) in the diet. All cows were managed in a normal production operation and health status was assessed by recording the incidence of health problems during the experimental period of wks 6 before and 16 after calving (-6 to 16 wks). Mastitis-related parameters included somatic cell counts (SCC), bacterial colony counts of milk samples from each mammary gland quarter of all cows during wk 1 to wk 8 postpartum. Peripheral blood neutrophil phagocytic function of eight cows fed either control or supplemental Cr diet was determined by the ability to take up uniform fluorescent beads measured by flow cytometry. Supplemental Cr had no effect (P > 0.10) on health status of cows during late pregnancy and early lactation, or on SCC and bacterial colonies of quarter milk samples from early lactation (wks 1 to 8). Supplemental Cr also did not affect neutrophil phagocytic function of cows from 6 wks prepartum to 6 wks postpartum. However, in the in vitro study of PBL (from control animals, not fed Cr diet) blastogenesis with addition of insulin or cortisol at two levels (0.05 and 0.5 ng ml-1), insulin and cortisol enhanced or had no effect on PBL proliferations with or without concanavalin A (con A) simulation. However, further Cr addition in the culture medium containing supplemental insulin or cortisol, particularly CrCl3, additively increased (P < 0.05) BPL blastogenic activities with or without con a stimulation. Conversely, addition of rBST or IFG-1 (0.5 and 5.0 ng ml-1) in the culture medium enhanced PBL proliferation, but addition of Cr gave no additional effect. These results indicated that supplemental Cr had no beneficial effect on health status, mastitis-related parameters or neutrophil phagocytic activity of dairy cows. However, in vitro study confirmed and extended our previous observations that Cr has an effect on lymphocyte proliferation and this may associate with insulin or cortisol actions.