Propionate as a precursor of milk constituents in the intact dairy cow.

The importance of propionate in intermediary metabolism is generally recognized (1). Reid (2) concludes from his work on sheep that for these animals propionic acid is the chief source of blood glucose. Similarly McClymont (3) suggests that ruminants in general maintain their blood sugar level by gluconeogenesis from propionic acid. Injection of C14-labeled propionate into a cow’s blood stream enabled us to measure the rate at which this metabolite is oxidized by a normal intact cow and to investigate the part it plays in the synthesis of milk constituents.