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Relationship Between Adenylate Energy Charge, Rumen Volatile Fatty Acid Concentrations, and Rates of Production and Dry Matter Digestibility in the Cow¹

Animal Research Institute, Research Branch, Agriculture Canada, Ottawa, Ontario, Canada, K1A 0C6

ABSTRACT

Adenylate energy charge [adenosine-5'-triphosphate + .5 adenosine diphosphate ÷ (adenosine 5'-tri-, +-di +-mono-phosphate)] was determined in a switch back experiment in which four diets ranging in dry matter digestibility from 36.7 to 67.6% were each fed in turn to four 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 .681, .738, .773, and .827, corresponding to dry matter digestibilities of 36.7, 48.2, 61.6, and 67.6%. The correlation coefficient between these two was .847. Dry matter digestibility also 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 also 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 also might serve as a useful indicator of diet digestibility.

¹ Contribution No. 889 from the Animal Research Institute.