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 supplement al dietary chromium (Cr) on health status and mastitis-related paramet ers, as well as neutrophil phagocytic activity of dairy cows during la te pregnancy and early lactation. In addition, possible interactions a nd involvements of Cr with insulin, cortisol, somatotropin (rBST) and insulin-like growth factor-1 (IGF-I) were directly investigated in vit ro 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 cal ving dates were randomly assigned to treatments: control and supplemen tal chelated Cr (0.5 ppm) in the diet, All cows were managed in a norm al production operation and health status was assessed by recording th e incidence of health problems during the experimental period of wks 6 before and 16 after calving (-6 to 16 wks), Mastitis-related paramete rs 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 eigh t cows fed either control or supplemental Cr diet was determined by th e ability to take up uniform fluorescent beads measured by flow cytome try, Supplemental Cr had no effect (P > 0.10) on health status of cows during late pregnancy and early lactation, or on SCC and bacterial co lonies of quarter milk samples from early lactation(wks 1 to 8). Suppl emental Cr also did not affect neutrophil phagocytic function of cows from 6 wks prepartum to 6 wks postpartum, However, in the in vitro stu dy of PBL (from control animals, not fed Cr diet) blastogenesis with a ddition 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 cor tisol, particularly CrCl3, additively increased (P < 0.05) PBL blastog enic activities with or without con A stimulation. Conversely, additio n of rBST or IGF-I (0.5 and 5.0 ng ml(-1)) in the culture medium enhan ced PBL proliferation, but addition of Cr gave no additional effect. T hese results indicated that supplemental Cr had no beneficial effect o n 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 prolife ration and this may associate with insulin or cortisol actions.