Effects of food deprivation on ketonaemia, ketogenesis and hepatic intermediary metabolism in the non-lactating dairy cow

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Abstract
Why non-lactating dairy cows [Friesian and Ayrshire] are less susceptible to the development of ketonemia during food deprivation than dairy cows in early lactation was investigated. The 1st experiment (expt. A) consisted of determining the effect of 6 days of food deprivation on the concentrations of ketone bodies, and of metabolites related to the regulation of ketogenesis, in jugular blood and liver of non-lactating cows. During the food deprivation, blood ketone-body concentrations rose significantly, but to a value that was only 16% of that achieved in lactating cows deprived of food for 6 days. In the liver, food deprivation caused a rise in ketone-body concentrations, a fall in the concentration of glycogen and of various intermediates of the Embden-Meyerhof pathway and the tricarboxylic acid cycle, an increase in cytoplasmic reduction, a decrease in the [total NAD+]/[total NADH] ratio and a decrease in energy charge. These changes were all qualitatively similar to those previously observed in the livers of the food-deprived lactating cows. A discrepancy in the food-deprived non-lactating cows appeared between the absence of marked ketonemia and the occurrence of metabolic changes within the liver, suggesting increased hepatic ketogenesis. This discrepancy was partially resolved in expt. B by the observation in 2 catheterized non-lactating cows that, although there was a 2-fold increase in hepatic ketogenesis during 6 days of food deprivation, ketogenesis from the splanchnic bed as a whole (i.e., gut and liver combined) declined slightly owing to cessation of gut ketogenesis.