Net portal absorption of lactate and volatile fatty acids in steers experiencing glucose-induced acidosis or fed a 70% concentrate diet ad libitum.

Five crossbred steers (347 kg) were surgically fitted with rumen fistulae, hepatic portal, abdominal aorta and mesenteric catheters to measure organic acid absorption from the gut during acute [intraruminal glucose, 12 g/kg body weight (G)] or subacute [ad libitum 70% concentrate diet (C)] acidosis. Samples were taken at time 0, then every 2 h for 48 h after a switch from an alfalfa diet to C, or dosing with G. Steers receiving C received G 1 wk later so that five steers provided four observations/treatment. Blood flow rates were determined by infusion of para-amino hippuric acid (PAH) and averaged 767.8 and 712.5 liters/h for C and G, respectively. Animals consuming C averaged 13.6 kg dry matter from 0 to 24 h and 1.5 kg from 24 to 48 h. Rumen pH declined to 4.2 for G compared with 6.0 for C. Blood pH and HCO3 showed only slight depressions for G from 16 to 26 h, the period of lowest rumen pH. Rumen L-lactate concentration averaged 53.4 mM (peak 77 mM) and 2.1 mM for G and C, respectively. Rumen D-lactate concentration averaged 30.2 mM (peak 47 mM) for G and 1.2 mM for C. Net portal absorption of L-lactate averaged 96.6 and 164.4 mmol/h, whereas that of D-lactate averaged 10.5 and 71.8 mmol/h for C and G, respectively. Mean net portal volatile fatty acid absorptions were 442.8, 192.1, 53.8, 5.3 and 10.4 mmol/h (C) and 100.0, 47.2, 9.4, .98 and .78 mmol/h (G) for acetate, propionate, butyrate, isobutyrate and isovalerate, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)