Insulin-dependent whole-body glucose utilization and insulin-responses to glucose in week 9 and week 19 of lactation in dairy cows fed rumen-protected crystalline fat or free fatty acids

Whole-body insulin-dependent glucose utilization and insulin responses to glucose in euglycemic-hyperinsulinemic clamps (EHGC) and in hyperglycemic clamps (HGC) were evaluated in high yielding dairy cows fed rumen-protected fat (triglycerides), free fatty acids, or a starch-rich ration (n = 5 per group) in Week 9 and Week 19 of lactation. The experiment was performed under conditions of nonsignificant differences in energy and protein balances in Week 9 and Week 19 and in the three groups. Basal (pre-infusion) concentrations of glucose were lower (P < 0.05) in Week 9 than in Week 19 of lactation and were higher (P < 0.05) in Week 9 in cows fed free fatty acids than in cows fed the starch-rich ration. In EHGC, glucose infusion rates were similar in Week 9 and Week 19 and in the different groups, indicating similar insulin-dependent glucose utilization. Furthermore, because insulin concentrations in EHGC in Week 9 and Week 19 and in the three groups were very similar, metabolic clearance rates of insulin were not affected by stage of lactation and feeding. In addition, insulin responses to the same glucose increments in HGC were not different in Week 9 and Week 19 and in the three groups, indicating that insulin secretion was not affected by stage of lactation and feeding. In conclusion, insulin secretion, insulin metabolic clearance rate, and insulin-dependent glucose utilization between Week 9 and Week 19 of lactation were stable. Furthermore, feeding rumen-protected triglycerides or free fatty acids did not significantly modify insulin secretion, insulin metabolic clearance rate and glucose-dependent glucose utilization compared with starch-rich feeding.