Comparison of glucose biokinetics in parturient ewes and ewes induced to lactate artificially

Glucose biokinetics of six normal pregnant/lactating ewes during the periparturient period were compared with those of five non-pregnant ewes induced to lactate artificially by treatment with oestrogen and progesterone, followed by a series of infusions of oxytocin. Normal ewes produced large amounts of milk (800-900 g/day) on day 1, and yields remained relatively constant until day 8 post partum. Milk production of induced ewes, however, was negligible on day 1 (30 g/day) but increased progressively until day 8 (540 g/day) after the start of milking. The glucose irreversible loss per minute 2-8 days before (6.4 v. 5.6 mg per kilogram body weight 0.75), and 2 days after the onset of lactation (9.1 v. 5.5 mg/min per kg0.75) was significantly greater (P less than 0.05) in normal pregnant/lactating ewes than in ewes induced to lactate artificially. By the eighth day of lactation rates of glucose irreversible loss per minute (7.4 v. 6.4 mg per kilogram body weight 0.75) were not significantly different (P greater than 0.05). The data were consistent with the hypothesis that glucose supply is rate limiting for milk production for several days after the initiation of lactation in non-pregnant, hormone-treated ewes. In parturient ewes, the rate of glucose irreversible loss was significantly increased 1-2 days post partum.