Relationship Between Adenylate Energy Charge, Rumen Volatile Fatty Acid Concentrations, and Rates of Production and Dry Matter Digestibility in the Cow

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Abstract
Adenylate energy charge [ATP + 0.5 ADP .div. (ATP + ADP + AMP)] was determined in a switch back experiment in which 4 diets ranging in dry matter digestibility from 36.7-67.6% were fed to 4 nonlactating Holstein cows. Adenylate energy charges determined on rumen samples taken via stomach tube 1 h after a once daily feeding of a maintenance ration were 0.681, 0.738, 0.773 and 0.827, corresponding to dry matter digestibilities of 36.7, 48.2, 61.6 and 67.6%. The correlation coefficient between these 2 was 0.847. Dry matter digestibility was significantly correlated with adenine nucleotide concentrations, total microbial cell counts, total rumen volatile fatty acid concentration and butyric acid concentration. Butyric was the only volatile fatty acid to show significant correlation of concentration and rate of production with energy charge, adenine nucleotide concentrations and microbial cell numbers. Butyric acid was the only volatile fatty acid whose concentration in the rumen was significantly correlated with its rate of production. Energy charge measured in rumen samples taken via stomach tube may be a measure of metabolic activity of the rumen microbial population and might serve as a useful indicator of diet digestibility.