Glucose entry rate in dairy cattle as determined by stable isotope 13C-labelled glucose at different stages of reproduction.

1. Uniformly labelled stable 13C-glucose was used to study glucose entry in high yielding Holstein cows (n = 8) under normal production conditions. 2. The single injection technique was repeated at three different reproductive phases. A two compartment model was applied to calculate mean entry rates of glucose resulting in: (1) Terminal phase of pregnancy (2 weeks a.p.): 0.41 g/hr/kg0.75; (2) Peak lactation (6 weeks p.p.): 0.97 g/hr/kg0.75; (3) End of lactation (37 weeks p.p.): 0.61 g/hr/kg0.75. 3. Data from studies using radioactively labelled tracers are in good agreement with our results obtained without any restrictions implied by the handling with radioactive substances.