Glucose metabolism and insulin sensitivity in Gulf Coast Native and Suffolk ewes during late gestation and early lactation

Abstract

Two experiments were conducted to evaluate possible differences in glucose metabolism and insulin responsiveness in Gulf Coast Native (GCN) and Suffolk (SFK) ewes. In Experiment 1, 30 GCN and 41 SFK ewes in late gestation were used to identify hyperglycemia and hyperinsulinemia. Blood samples were obtained via jugular venipuncture and analyzed for plasma insulin, glucose, thyroxine, albumin, and plasma urea nitrogen (PUN) concentrations. In Experiment 2, at 2-week postpartum, 19 GCN and 19 SFK ewes were administered frequently sampled intravenous glucose tolerance tests (FSIGT) consisting of a pulse dose of glucose (500 mg kg −1 BW) followed by an infusion of insulin (0.03 IU kg −1 BW). Blood samples were collected via jugular catheter at timed intervals over a 3 h period after glucose infusion. Samples from the FSIGT were analyzed for insulin and glucose concentrations, and the minimal model computer program was then used to assess glucose effectiveness ( S G), an estimate of insulin-independent glucose disappearance; insulin sensitivity ( S I), an estimate of insulin-dependent glucose disappearance; and acute insulin response (AIR glucose), insulin secretion relative to glucose administration. Concentrations of albumin, thyroxine, and PUN were measured in samples collected prior to glucose infusion. In Experiment 1, insulin concentrations were greater ( P<0.01) in SFK ewes while plasma glucose concentrations were not different between breeds. Concentrations of albumin ( P<0.01), thyroxine ( P<0.05), and PUN ( P<0.05) were greater in SFK ewes. In Experiment 2, S G and S I did not differ between breeds, while AIR glucose tended to be greater in GCN ewes. There were no differences in plasma albumin, thyroxine, or PUN concentrations. These data indicate slight differences in insulin sensitivity between GCN and SFK ewes during late gestation. However, there were no apparent differences in glucose metabolism between these breeds during the early lactation period.