Three modes of metabolism, indicative of differing levels of
carbohydrate sufficiency, can be identified in nonpregnant dairy cows. The metabolic parameters defining these modes include: the hepatic content of
glycogen and glucogenic metabolites; the in vivo net exchange of
glucose and
propionate across the liver, and of
lactate and
pyruvate across the liver and gut; and the concentration of
insulin in the blood, and the secretion rate of
insulin. In descending order of
carbohydrate sufficiency, the three modes are; mode I, seen in fed nonlactating cows; mode 2, seen in fed lactating cows; and mode 3, seen in fasted or ketotic cows. The modes are interconvertible, because fasting will transform modes 1 or 2 into mode 3, while administration of either
glucose,
propionate, or
glucocorticoid will, on the basis of at least one index, transform modes 2 or 3 into mode 1. It is concluded that a)
carbohydrate sufficiency is jeopardized in lactating cows, and b) one reason for the therapeutic efficacy of antiketogenic agents used in the treatment of bovine
ketosis is the ability of these compounds to increase
carbohydrate sufficiency.