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Effect of Diet and Glucocorticoid Administration on Liver Phosphoenolpyruvate Carboxykinase Activity in the Dairy Cow

Department of Animal Science, Cornell University, Ithaca, New York 14850

ABSTRACT

The liver phosphoenolpyruvate carboxykinase activity and blood glucose and ketone concentrations of 18 dairy cows were determined at 6 weeks prepartum, during the first week postpartum, and during the sixth week postpartum. Six of the cows were assigned to each of 3 treatments : a) hay ad libitum up to parturition supplemented with restricted concentrate (15% protein) during lactation; b) restricted hay plus concentrate (15% protein) to appetite immediately before parturition and during lactation; and c) same as b with a 24% protein concentrate. The only significant change in liver phosphoenolpyruvate carboxykinase activity was a reduction in the activity of the cows on Treatment A during the first week postpartum. At the same time blood glucose was depressed and blood ketones elevated. The liver enzyme activity was positively correlated with digestible dry matter intake, crude protein intake, milk production and body weight.

Three days of reduced feed intake tended to depress the liver phosphoenolpyruvate carboxykinase activity of lactating cows. The liver enzyme activity was reduced in both lactating and nonlactating cows 18 hours after the administration of a glucocorticoid hormone. At the same time blood glucose was increased up to twofold.

¹ Present address: The Agricultural Institute, Moorepark, Fermoy, Co. Cork, Ireland.

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