Net metabolism of volatile fatty acids, D-beta-hydroxybutyrate, nonesterifield fatty acids, and blood gasses by portal-drained viscera and liver of lactating Holstein cows.

Net flux of VFA, D-beta-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-beta-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 portal-drained visceral flux of VFA, D-beta-hydroxybutyrate, alpha-amino nitrogen, L-lactate, and oxygen together accounted for 84.9% of calculated metabolizable energy intake. Net hepatic removal of propionate, L-lactate, and alpha-amino nitrogen maximally accounted for 55.1, 17.4, and 16.5% of carbon in glucose produced by hepatic tissues.