Effect of normal and high manganese diets on the role of bile in manganese metabolism of calves.

The role of bile in manganese metabolism and homeostasis was studied in Holstein bull calves fed diets containing 32 ppm manganese (normal) (control) or 1,000 ppm supplemental manganese (high-manganese) for 2 weeks before and 1 week after intravenous (IV) and duodenal S4Mn dosing. After dosing, all the bile was collected at 15 and 60 minutes, hourly to 12 hr and daily to 7 days. All calves were sacrificed 7 days after dosing to determine the tissue S4Mn distribution. High-Mn-fed calves secreted 48% of the IV S4Mn dose in bile over the 7-day period; which was 12 times that in bile of control calves. In contrast, after duodenal dosing, only a very small amount of S4Mn was secreted in bile by either control (.32%) or high-Mn-fed (.30%) calves over the 7-day period. With both methods of dosing, calves fed the high-Mn diets had a lower average S4Mn concentration in most tissues taken than calves fed the control diet. These data from IV dosing confirm earlier work that excretion and tissue distribution of injected S4Mn is very sensitive to dietary Mn. The data from duodenally-dosed calves showed that the amount of Mn absorbed is decreased by higher dietary Mn intake. In contrast to previously held theory, enterohepatic circulation of Mn apparently plays only a minor role in homeostasis of fed Mn. Manganese homeostasis in calves appears to be the result of changes both of absorption and