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Net Metabolism of Volatile Fatty Acids, D-ß-Hydroxybutyrate, Nonesterified Fatty Acids, and Blood Gasses by Portal-Drained Viscera and Liver of Lactating Holstein Cows^{1, 2,}

Department of Animal Science, University of Maryland, College Park 20742

Gerald B. Huntington, Henry F. Tyrrell and Paul J. Reynolds

USDA, ARS Livestock and Poultry Sciences Institute, Ruminant Nutrition Laboratory, Beltsville, MD 20705

ABSTRACT

Net flux of VFA, D-ß-hydroxybutyrate, nonesterified fatty acids, and blood gasses across portal-drained viscera and liver was measured in four lactating Holstein cows fed a 60:40 corn silage: concentrate diet ad libitum and milked at 12-h intervals. Twelve consecutive hourly measurements of net flux (venous-arterial concentration difference times blood flow) were obtained during wk 4 and 8 postpartum for each cow. Milk yield and DM intake averaged 32.2 and 15.6 kg/d. On a net basis, hepatic tissues produced acetate and removed 63 to 101% of other VFA absorbed by portal-drained viscera. Hepatic and portal-drained visceral tissues produced 60 and 40%, respectively, of D-ß-hydroxybutyrate produced by splanchnic tissues. Hepatic tissues removed 9.3% of non-esterified fatty acids in portal vein and hepatic arterial blood. Oxygen use was greater by liver than for portal-drained viscera (3062 vs. 2394 mmol/h). Net portal-drained visceral flux of VFA, D-ß-hydroxybutyrate, -amino nitrogen, L-lactate, and oxygen together accounted for 84.9% of calculated metabolizable energy intake. Net hepatic removal of propionate, L-lactate, and -amino nitrogen maximalley accounted for 55.1, 17.4, and 16.5% of carbon in glucose produced by hepatic tissues.

¹ Mention of a trade name, proprietary product, or specific equipment does not constitute a guarantee or warranty by the US Department of Agriculture and does not imply its approval to the exclusion of other products that may be suitable.

² Scientific Article Number A-4731, Contribution Number 7727 of the Maryland Agricultural Experiment Station, Department of Animal Sciences.

³ Present address: Ruminant Nutrition Laboratory, USDA, ARS, BARC-East, Beltsville, MD 20705.

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