Portal recovery of short-chain fatty acids infused into the temporarily-isolated and washed reticulo-rumen of sheep

The present study was undertaken to study the metabolism of short-chain fat ty acids (SCFA) by the reticulo-ruminal epithelium and the portal-drained v iscera (PDV) under in vivo conditions with no interference from the metabol ism of the rumen microbes. The technique of temporary isolation of the reti culo-rumen was applied to wethers implanted with catheters in a mesenteric artery, the hepatic portal vein and the right ruminal vein. Portal blood fl ow was measured by downstream dilution of p-aminohippuric acid; the PDV upt ake of arterial acetate, as well as the whole-body irreversible loss rate ( ILR) of acetate, was estimated by [2-C-13]acetate infusion into the right r uminal vein. The sheep were maintained with a bicarbonate-buffered solution of SCFA in the reticulo-rumen along with continuous intraruminal infusion of SCFA for 4 h. The portal appearance of SCFA of non-reticulo-ruminal orig in was estimated before and after the infusion protocol. Of the acetate abs orbed by the sheep, 89 (SE 5), 109 (SE 7) and 101 (SE 7) % was recovered as portal net appearance of acetate, portal net appearance of acetate correct ed for PDV uptake of arterial acetate and increase in the ILR of acetate re spectively. Of the propionate, isobutyrate, butyrate, isovalerate and valer ate absorbed by the sheep, 95 (SE 7), 102 (SE 9), 23 (SE 3), 48 (SE 5) and 32 (SE 4) % respectively was recovered as portal net appearance. In contras t to current concepts, the present study showed that the reticulo-ruminal e pithelium metabolizes none (or only a small proportion) of the acetate and propionate absorbed from the rumen. This observation could lead to the more efficient use of results obtained with multi-catheterized animals to quant ify the net metabolite output of the rumen microbes.