Two glucose clamp techniques were performed for 6 h starting 2 h before the initiation of feeding to investigate the effect of dietary propionate supplementation on insulin responsiveness to glucose and tissue responsiveness to insulin in relation to feeding in rams. The rams were fed alfalfa hay without (Cont diet) and with 10 mmol.kg BW-1.d-1 of calcium propionate (Prop diet) for 4 weeks in randomized order. With the hyperglycemic clamp, the ratio of plasma insulin increment to glucose infusion rate did not differ between the diets, but for the Prop diet the ratio was less during the pre-feeding period. With the hyperinsulinemic euglycemic clamp, the glucose infusion rate was lower (P < 0.05) for the Prop diet than the Cont diet, and increased (P < 0.05) after feeding. In rams supplemented propionate tissue responsiveness to insulin was reduced. Propionate supplementation may either impair glucose utilization in response to insulin infusion or enhance glucose production from propionate.