The impact of the chromium supplementation on insulin signalling pathway in different tissues and milk yield in dairy cows

Thirty days before expected time of parturition, 20 Holstein cows were divided into -Cr and +Cr groups. From day 25 before parturition (BP) up to day 30 after parturition (AP), +Cr cows received 10 mg of Cr (chromium-enriched yeast) daily. Muscle and adipose tissue samples were taken at days -30, -10, +7 and +10 related to parturition, when body condition score (BCS) was also determined. Hepatic tissue samples were taken at days -10 and +7. Tissue samples were used for determination of the insulin signalling pathway protein expressions. Intravenous glucose tolerance test (IVGTT) was performed at days -28, -7, +10 and +30. Milk yield was recorded during first 14 weeks AP. Milk composition was obtained at days 7 and 28 AP. At day 10 BP, protein content of beta-subunit of insulin receptor (IR beta) was significantly higher (p < 0.05) in muscle, and phosphorylation of insulin receptor substrate 1 at serine 307 (pIRS-1 Ser(307)) was significantly lower (p < 0.05) in hepatic tissue of +Cr group. After parturition, pIRS-1 Ser(307) was significantly lower in muscle tissue at days 7 and 28 (p < 0.05 and p < 0.001, respectively), while phosphorylation of Akt at serine 473 (pAkt Ser(473)) was significantly higher (p < 0.01) in hepatic tissue at day 7 AP in +Cr group. Chromium had opposite effect on insulin kinetics during IVGTTs obtained BP and AP. Insulin secretion was significantly reduced at day 7 BP and significantly enhanced at day 10 AP, when NEFA concentration was also significantly increased. Milk yield and ECM value were depressed in +Cr group. DMI and BCS were significantly enhanced in +Cr group at day 7 BP. In conclusion, chromium modulates insulin signalling pathway in dairy cows, but targeted signalling molecules are different in antepartal then post-partal period, probably due to duration of exposure to chromium and different energy status between those periods.