PRODUCTION RESEARCH PAPERS Net Metabolism of Volatile Fatty Acids, D-(/-Hydroxybutyrate, Nonesterified Fatty Acids, and Blood Gasses by Portal-Drained Viscera and Liver of Lactating Holstein Cows 1'2

Net flux of VFA, D-~-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 (venousarterial 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 portaldrained viscera. Hepatic and portaldrained visceral tissues produced 60 and 40%, respectively, of D-~-hydroxybutyrate produced by splanchnic tissues. Hepatic tissues removed 9.3% of nonesterified 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