Effects of excessive energy intake and supplementation with chromium propionate on insulin resistance parameters in lactating dairy cows: II. Glucose tolerance tests and follicular flushing

Abstract Text: The objective of this experiment was to compare insulin resistance parameters and reproductive outcomes 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. Glucose tolerance tests (GTT) were performed on d 40, 82, 124, 166, and 208 by infusing cows with 0.5 g of glucose/kg of BW, whereas blood samples were collected at -15, 0, 10, 20, 30, 45, 60, 90, and 120 min relative to infusion for determination of serum insulin and glucose. Follicle aspiration for in vitro embryo production was performed 2 d after each GTT. No treatment effects were detected (P = 0.53) for serum glucose concentrations. Treatment x min interactions (P < 0.01) were detected for serum insulin and insulin:glucose ratio, given that these parameters were greater (P ≤ 0.05) for HIGH compared with HIGHCR and MAN from 10 to 60 min relative to glucose infusion, but always similar between HIGHCR and MAN (P ≥ 0.25). A treatment x parity interaction was detected for oocyte collection (P = 0.05). Within multiparous cows, HIGHCR had greater (P ≤ 0.03) number of viable oocytes collected compared with HIGH and MAN, whereas the same outcome was not detected (P ≥ 0.36) within primiparous cows. No treatment effects were detected (P ≥ 0.33) for number of embryos produced, or oocyte collected:embryo produced ratio. In conclusion, Cr-propionate supplementation prevented the increase in insulin resistance caused by excessive energy intake in lactating dairy cows during a GTT, and increased the number of viable oocytes collected during follicle aspiration for in vitro embryo production.

Keywords: Chromium, dairy cows, energy, insulin resistance