Comparison of measurements of glucose flux rates in wethers and in pregnant and lactating ewes using 14C and 3H labelled tracers

Abstract

Glucose flux rates (GFR) were determined, from plateau glucose specific radioactivity values obtained during continuous infusions of [U - 14C] + [2 - 3H], [U - 14C] + [3 - 3H] and [U - 14C] + [6 - 3H] glucose tracers, in wethers fed either 800 g per day of poor quality hay plus 400 g barley per day. GFR determined with [U - 14C] glucose ranged from 15 to 24 mmoles per hour on the hay diet and from 22 to 34 mmoles per hour on the hay plus barley diet. The variation in GRF within animals and between days accounted for most of the total variability. GFR determined with [6 - 3H] glucose were similar to those estimated with [U - 14C] glucose but those determined with [2 - 3H] and [3 - 3H] glucoses were 14 per cent higher. GFR were also determined with [U - 14C] + [6 - 3H] glucose tracers in pregnant ewes fed 1000 g medium quality hay plus 400 g concentrate and in lactating ewes fed different amounts of medium quality hay plus concentrate. GFR, determined with [U - 14C] glucose, ranged from 27 to 49 mmoles per hour in pregnancy and from 54 to 83 mmoles per hour in lactation. At approximately 125 days' gestation there was a significant positive relationship between GFR and total lamb birth weight. Estimates of GFR with [6 - 3H] glucose were 21 per cent higher in pregnancy and 15 per cent higher in lactation than the simultaneous estimates with [U - 14C] glucose.