Partition of portal-drained visceral net flux in beef steers. 2. Net flux of volatile fatty acids, D-beta-hydroxybutyrate and L-lactate across stomach and post-stomach tissues.

1. Net flux of volatile fatty acids (VFA), D-beta-hydroxybutyrate (BOHB) and L-lactate across post-stomach (anterior mesenteric-drained viscera (MDV], stomach and total hepatic portal-drained viscera (PDV) tissues was measured in two beef steers (mean live weight 390 kg). 2. Net flux was measured while steers were fed, in sequence, on (1) chopped lucerne (Medicato sativa) (twelve meals/d), (2) chopped lucerne (two meals/d) and (3) a pelleted concentrate diet containing 780 g ground maize/kg (two meals/d). 3. Five hourly net flux measurements were obtained on 2 d for each dietary regimen, beginning 0.5 h before a meal delivered at 08.00 hours. Net flux was calculated as venous-arterial concentration differences (VA) multiplied by blood flow (measured by downstream dilution of p-aminohippurate (PAH]. 4. Stomach tissues accounted for 85 to over 100% of net VFA and BOHB appearance across PDV. Net appearance across stomach tissues represented 74% of net PDV L-lactate appearance. 5. When lucerne was given, there was net utilization of arterial acetate and BOHB across MDV. This MDV utilization may reflect acetate and BOHB use as an energy source or their incorporation into mesenteric fat. 6. When concentrate was given, more n-butyrate and n-valerate and less L-lactate appeared across PDV and less 3-methylbutyrate appeared across stomach tissues than when lucerne was given. Postprandial increases in VFA, BOHB and L-lactate net flux across PDV followed meal-feeding of lucerne. 7. On a net basis, the relative contribution of MDV tissues of total PDV net appearance of VFA and BOHB was small (less than 15%) in these steers.