Glucose metabolism in lactating reindeer

Changes in glucose synthesis during the lactation cycle were estimated in pen-fed and grazing reindeer. The pool size, space, transfer rate, and irreversible loss of glucose were determined using simultaneous injections of [2-3H]glucose and primed infusions of [U-14C]glucose in reindeer lactating for 1–2, 4–5, 8–9, and 12–16 weeks. Glucose transfer rate and irreversible loss were higher during early to midlactation than at other times of the year; maximum estimates were at 8–9 weeks postpartum (July), and a decline was noted at 12–16 weeks (August). During the first 1–2 weeks in pen-fed and 4–5 weeks in grazing reindeer, glucose transfer rate and irreversible loss were almost twice the values reported for reindeer at maintenance. No difference in the irreversible loss of glucose was noted between lactating and non-lactating reindeer at 18–20 weeks postpartum (September), and there is evidence that this may occur as early as 12–16 weeks postpartum. No significant trend was noted in the glucose space throughout lactation; however, a significant increase in plasma glucose concentration and pool size was noted when glucose synthesis was highest (8–9 weeks postpartum). Glucose turnover time was consistently faster (78–88 min) in lactating than in non-lactating reindeer (107–140 min). Reindeer used a smaller proportion of plasma glucose-C for lactose synthesis than did other domestic species. This probably results from the low lactose content of reindeer milk and the relatively low rate of milk secretion.