Metabolism of Acetate, Propionate, and N-Butyrate in Young Milk-Fed Calves

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Abstract
The metabolism of acetate-1-C14, propionate-1-C14 and n-butyrate-l-C14 was studied in milk-fed calves up to 80 days of age. Quantities of each acid calculated to supply one-half of maintenance energy were infused intravenously for 8 hours. During the infusion, expired air was monitored for C14O2, and venous blood was sampled for the isolation of metabolic intermediates. The expired CO2 derived from the oxidized portion of the infused acids was between 20 and 30% of total expired CO2, indicating that the acids could be metabolized in relatively large quantities by young calves. There were no significant differences in rates of metabolism attributable to individual acids or to age. Acetate, propionate, and butyrate appeared to be metabolized largely by established pathways. Acetate and butyrate resulted in increased ketone production while propionate caused a decreased production. Propionate and butyrate contributed about equally, but greater than acetate, to blood glucose labeling. Infusion of all acids resulted in decreased blood glucose levels, and increased blood lactate levels. During infusions of acetate and butyrate, both the concentration and the specific activity of blood malic acid increased, suggesting the presence of at least a portion of the glyoxylate pathway.