SCFA TRANSPORT IN THE FORESTOMACH OF RUMINANTS

Short-chain fatty acids are the main end-products of microbial metabol ism in the forestomach of ruminants. SCFA produced by the microorganis ms are rapidly absorbed across forestomach epithelia and can cover up to 80% of the energy requirement of the animal. Although there is a gr eat concentration gradient for SCFA between the forestomach content an d the blood favoring passive transport, (secondary) active transport m echanisms are likely involved in SCFA permeation across the epithelia. (Secondary) active SCFA transport seems to be mediated by an anionic exchange system. The system interacts with other anions like chloride and bicarbonate. Similar to the large intestine of various species, SC FA can stimulate sodium transport probably by activating a Na+/H+ exch ange located in the apical membrane. However, in contrast to the large intestine, SCFA transport itself seems to be independent from sodium. Part of the absorbed SCFA does not reach the blood side in the origin al form because it is metabolized in the epithelial cell. Metabolism, in turn, influences SCFA transport. (C) 1997 Elsevier Science Inc.