SHORT-CHAIN FATTY-ACIDS IN SHEEP - PORTAL APPEARANCE RATES FOLLOWING HIGH INTRARUMINAL LOADS

The portal recovery of SCFA (short-chain fatty acids) infused intrarum inally 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 us ed. Portal and arterial blood as well as rumen liquid was sampled duri ng a period of 450 min following the loads. The PDV (portal-drained vi scera) metabolism of arterial acetate and the ILR (irreversible loss r ate) of arterial acetate were estimated by intravenous infusion of sod ium-acetate [l- C-13]. The portal blood flow rate was measured using u ltrasonic transit time flow probes. The portal blood flow rate increas ed by 60-70% following the intraruminal loads of SCFA compared with th e 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 conc entrations as high as 3.5, 1.0 and 0.7 mmol l(-1) of acetate, propiona te and butyrate, respectively, were measured following the loads. The portal appearance of SCFA appeared to be down-regulated during the per iod from 20-120 min following the load of 2.4 :mol SCFA. The portal re covery of infused acetate and propionate decreased with increasing amo unts of infused SCFA. Recoveries were estimated as 0.46 to 0.59 for ac etate, 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 increas ed (0.05 +/- 0.02) when the sheep were adapted to the CS diet (P < 0.0 5). A model of the regulation of SCFA absorption from the rumen implic ating a role of peripheral butyrate is discussed in the context of the results from the present study and from literature data.