Glucose tolerance in ewes and susceptibility to pregnancy toxaemia

Intravenous glucose tolerance tests were undertaken on fed twin-pregnant ewes at about 120 days of gestation by injecting 0.4 g glucose per kilogram of live weight, then measuring glucose and insulin concentrations in plasma over the next 2 h. An insulin resistance index was calculated from the product of T1/2 for glucose disappearance and the plasma insulin concentrations integrated over time. Approximately 10 days later, the ewes were starved to induce ovine pregnancy toxaemia. During this period, the course of the hypoglycaemia and ketonaemia were followed by measuring metabolite concentrations in jugular blood samples obtained every 2-3 days. The existence of dehydration, acid-base imbalance and renal failure was also determined from packed cell volumes, serum CO2 content and serum concentrations of urea, creatinine and inorganic phosphate. Ewes that became recumbent and moribund with the disease were classified as susceptible whereas those asymptomatic after 10 days were classified as non-susceptible. Seven susceptible ewes had significantly higher insulin resistance indices (2043 +/- 670 s.d.) than did six non-susceptible ewes (1261 +/- 433 s.d.). It was concluded that poor control of glucose homeostasis may be an important predisposing factor in pathogenesis of the disease.