Changes in the blood flow to the digestive organs of sheep induced by feeding

The blood flow to the digestive organs of nine sheep was determined by the use of isotopically labelled microspheres before, during and at 2 h and 4 h after feeding. Within 3 min of the start of feeding, the blood flow to the salivary glands and to the smooth muscle of the rumen and reticulum increased three-fold. The blood flow to the epithelium of the rumen and reticulum also increased before any appreciable effect on ruminal fermentation could have occurred. This increase in flow was greater in absolute but smaller in relative terms than that to the muscle. At 2 h after feeding blood flow to the epithelium of the rumen and reticulum was two to four times greater than before food was taken, while the flow to the smooth muscle of these organs had fallen to the level found before feeding. In the more distal parts of the gastrointestinal tract, blood flow changes in response to feeding were less pronounced and, where they occurred at all, consisted of decreases at different times. Thus blood flow to the omasum decreased during feeding but recovered thereafter, while the flows to abomasum, duodenum and ileum were not changed during feeding but were significantly lower at 2 h and 4 h later. In the rest of the small intestine and in the large intestine there were no significant changes in flow during the period of observation, nor were there any changes in the blood flow to pancreas or spleen. However, the flow to the omental and mesenteric fat declined abruptly on feeding and reached its minimal value 2 h afterwards. These results are in marked contrast to those reported in other species in that the subepithelial capillary plexus of the reticulum and rumen was the only region contributing to the increased hepatic portal blood flow after feeding.