Mammary Blood Flow and Glucose Uptake in Lactating Cows Given Dexamethasone

Dexamethasone (two 10-mg intramuscular injections 12h apart) was given to three lactating cows. Milk production decreased from 13.0±1.9 to 8.5±2.2 kg/day (mean±standard error). Mammary blood flow estimated by the antipyrine absorption method decreased in four of six half udders following dexamethasone. Changes in packed cell volume and plasma concentrations of free fatty acids, calcium, and magnesium and blood L-lactate were not significant. Mean blood 3-OH-butyrate concentration decreased from 6.4 to 4.5 mg/100ml. Plasma glucose concentration increased from 58±3 to 107±9 mg/100ml. Mammary arteriovenous differences of glucose were decreased by 41% and net mammary uptakes of glucose by 38%. Milk production was correlated with the mammary arteriovenous difference, extraction and net uptake of glucose, and the net uptake of glucose-plus-lactate but not with arterial glucose concentration. The results associate diminished milk production with diminished glucose uptake and utilization of glucose by the mammary gland rather than diminished availability of glucose in the blood.