Effects of excessive energy intake and supplementation with chromium propionate on insulin resistance parameters in lactating dairy cows: I. Performance and weekly physiological measurements

Abstract Text: The objective of this experiment was to compare performance and insulin resistance parameters in lactating dairy cows with adequate or excessive energy intake, as well as in lactating dairy cows with excessive energy intake receiving Cr-propionate supplementation. Seventeen primiparous and multiparous, lactating Holstein cows were ranked by parity, BW, and BCS, and assigned to 1 of 3 dietary treatments on d 0: 1) diet to meet their NE_l requirements without Cr supplementation (MAN; n = 5), 2) diet to exceed their NE_l requirements without Cr supplementation (HIGH; n = 6), and 3) HIGH with 2.5 g/d of Cr-propionate (HIGHCR; n = 8, with 10 mg of Cr/cow daily). Cows were maintained in a single group and offered corn silage for ad libitum consumption, but received a corn-based concentrate twice daily via individual self-locking head gates from d 0 to 210. Concentrate intake was formulated to provide 100% of daily NE_l requirements of MAN and 160% of daily NE_l requirements of HIGH and HIGHCR cows. Cow BW, BCS, and milk production were recorded weekly. Blood samples were also collected weekly, prior to and at 2 and 4 h after the morning concentrate feeding, and analyzed for serum glucose, insulin, and NEFA. Pre-prandial revised quantitative insulin sensitivity check index (RQUICKI) was determined using serum glucose, insulin, and NEFA concentrations obtained prior to concentrate feeding.  No treatment effect was detected for BW change (P = 0.74), although BCS change from d 0 to 210 was greater (P = 0.02) in HIGH and HIGHCR compared with MAN. Milk production was similar between treatments (P = 0.92). Serum glucose concentrations and RQUICKI were also similar (P ≥ 0.68) across treatments, whereas mean serum NEFA concentrations (pre-prandial samples only) were greater (P = 0.04) for MAN compared with HIGH and HIGHCR. Treatment × parity × day interactions were detected (P < 0.01) for serum insulin and insulin:glucose ratio. These parameters were generally greater (P≤ 0.05) for HIGH, intermediate for HIGHCR cows, and lesser for MAN beginning on d 70 of the experiment for multiparous cow, and beginning on d 168 for primiparous cows. In conclusion, lactating dairy cows consuming excessive energy experienced reduced insulin sensitivity compared to cows consuming adequate amounts of energy, characterizing a state of insulin resistance, whereas Cr-propionate supplementation alleviated this outcome. However, milk production was not impacted by excessive energy intake or Cr-propionate supplementation.

Keywords: Chromium, dairy cows, energy intake, insulin resistance