EFFECT OF INTRARUMINAL PROPIONIC-ACID INFUSION ON METABOLISM OF MESENTERIC-DRAINED AND PORTAL-DRAINED VISCERA IN GROWING STEERS FED A FORAGE DIET .1. VOLATILE FATTY-ACIDS, GLUCOSE, AND LACTATE

This experiment investigated the effect of intraruminal infusion of pr opionic acid on ruminal VFA metabolism and the absorption of nutrients by the mesenteric- and portal-drained viscera of seven Friesian steer s, average BW 127 kg, fed a dried grass-pellet diet. Each received by random allocation 0 (control), .5, or 1.0 mol of propionic acid/d for 7 d. Ruminal acetate and propionate irreversible loss rates and carbon exchange between VFA and CO2 were measured during continuous intrarum inal infusions of 2-C-14-acetic acid and 2-C-14-propionic acid. Rumina l acetate irreversible loss rate was not affected by propionic acid in fusion (overall mean 8.09, error mean square [EMS] 2.68 mol/d), wherea s propionate irreversible loss increased incrementally with PA supply (3.22 vs 4.16, EMS .61 mol/d, for control and 1.0 mol of propionic aci d/d, respectively, P = .09). Glucose irreversible loss rate was increa sed at the highest level of PA infusion (2.84, 2.83, sind 3.22, EMS .0 6 mol/d, for control, .5, and 1.0 mol of propionic acid/d, respectivel y; P = .02 for control vs .5 + 1.0), although the proportion of glucos e irreversible loss derived from propionate remained constant (.6). Ne t absorption into venous blood showed that propionate was extensively metabolized in the rumen wall and that the tissues of the small intest ine utilized acetate. Utilization of glucose was reduced in portal tis sues as a result of intraruminal infusion, and the data were used to d erive a model of glucose and lactate interrelationships in gut tissues .