Key hormonal and metabolic control systems modifying nutrient use

Insulin sensitivity and responsiveness during lactation and dry period in goats

To investigate the role of insulin in partitioning nutrients between the mammary gland and other tissues during lactation in ruminants, euglycemic-hyperinsulinemic clamps were performed in goats during early lactation (15-26 days postpartum), midlactation (78-91 days postpartum), and dry period (169-194 days postpartum). Insulin was infused at 0.4, 0.7, 1.9, 4.4, and 10 micrograms/min. Basal plasma glucose was constant during all periods despite the fact that basal glucose utilization was approximately 3 times higher during lactation than dry period. Basal plasma insulin was similar during early lactation and dry period but increased during midlactation. Insulin infusion resulted in a dose-dependent stimulation of glucose utilization. The insulin-stimulated glucose utilization above basal was greatly impaired during early lactation when compared with dry period, but this only occurred at very high plasma insulin. Insulin infusion also resulted in a decrease in glucose production; the maximal insulin effect is achieved at the lowest insulin infusion rate. The ability of insulin to decrease glucose production was significantly improved during early lactation when compared with dry period. This phenomenon may provide a mechanism to save gluconeogenic substrates during early lactation. In contrast, midlactation did not result in any significant change in insulin action with both glucose utilization and glucose production.