Short-chain fatty acids in sheep: Portal appearance rates following high intraruminal loads

The portal recovery of SCFA (short-chain fatty acids) infused intraruminally as a single load was investigated in sheep adapted to a hay (H) or a concentrate/straw (CS) diet. The treatments were control (saline), 1.4 mol and 2.4 mol of SCFA (in % 65:20:15 acetate, propionate and butyrate). Three rumen cannulated and multi-catheterized sheep were used. Portal and arterial blood as well as rumen liquid was sampled during a period of 450 min following the loads. The PDV (portal-drained viscera) metabolism of arterial acetate and the ILR (irreversible loss rate) of arterial acetate were estimated by intravenous infusion of sodium-acetate [l- C-13]. The portal blood flow rate was measured using ultrasonic transit time flow probes. The portal blood flow rate increased by 60-70% following the intraruminal loads of SCFA compared with the preinfusion level. The portal recovery of arterial acetate increased to 0.84 +/- 0.02 and 0.95 +/- 0.01 in samples obtained 5 min after an intraruminal load of 1.4 or 2.4 mol SCFA, respectively. Arterial concentrations as high as 3.5, 1.0 and 0.7 mmol l(-1) of acetate, propionate and butyrate, respectively, were measured following the loads. The portal appearance of SCFA appeared to be down-regulated during the period from 20-120 min following the load of 2.4 :mol SCFA. The portal recovery of infused acetate and propionate decreased with increasing amounts of infused SCFA. Recoveries were estimated as 0.46 to 0.59 for acetate, 0.52 to 0.61 for propionate and 0.28 to 0.36 for butyrate. Only the recovery of acetate was affected by diet and the recovery increased (0.05 +/- 0.02) when the sheep were adapted to the CS diet (P < 0.05). A model of the regulation of SCFA absorption from the rumen implicating a role of peripheral butyrate is discussed in the context of the results from the present study and from literature data.