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 β-subunit of insulin receptor (IRβ) was significantly higher (p ˂ 0.05) in muscle, and phosphorylation of insulin receptor substrate 1 at serine 307 (pIRS-1 Ser307 ) was significantly lower (p ˂ 0.05) in hepatic tissue of +Cr group. After parturition, pIRS-1 Ser307 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 Ser473 ) 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.
Keywords: bovine; chromium; insulin signalling pathway.
© 2017 Blackwell Verlag GmbH.