Insulin responsiveness to glucose and tissue responsiveness to insulin during lactation in dairy cows.

The hyperglycemic clamp and hyperinsulinemic euglycemic clamp techniques were conducted to assess insulin responsiveness to glucose and tissue responsiveness to insulin in lactating and nonlactating Holstein cows. In the hyperglycemic clamp experiment, blood glucose concentrations were clamped at 50 mg/dl above the pre-infusion values by variable rates of glucose infusion. The mean plasma insulin increments over the baseline (insulin responsiveness to glucose) during hyperglycemia were lower (P < .05) in lactating cows than in nonlactating cows (23 vs. 102 microU/ml). In the hyperinsulinemic euglycemic clamp experiment, insulin was infused at the constant rate of 6.0 mU.kgBW-1.min-1 for 2 hr, and glucose was concomitantly infused at a variable rate to maintain the pre-infusion concentrations of blood glucose. Glucose infusion rates (tissue responsiveness to insulin) were similar (3.2 mg.kgBW-1.min-1) for lactating and nonlactating cows. It is concluded that insulin responsiveness to glucose is reduced, and tissue responsiveness to insulin remains unchanged during lactation in Holstein cows.