Effects of fiber laxatives and calcium docusate on regional water content and viscosity of digesta in the large intestine of the pig.

The aim of this study was to determine how bulk fibers and calcium docusate affect regional dehydration and digesta viscosity throughout the large intestine. Fifty-two pigs were fed a chow diet supplemented with a bulk laxative, placebo, or calcium docusate for three days, after which the pigs were sacrificed and the contents of the large bowel were analyzed. Digesta occurred as a continuum from liquid (cecum, 91.2% water content) to solid (rectum, 70.5% water content). The observed 20.7% difference in water content resulted in a 240-fold increase in viscosity. Half of this water is reabsorbed in the first 18% of the large bowel length where viscosity remains relatively low. Compared to placebo, calcium docusate and calcium polycarbophil had no significant effect on digesta water content or viscosity, polycarbophil exhibited significantly (P < 0.05) lower digesta viscosity in three bowel segments, and psyllium exhibited significantly (P < 0.01) lower viscosity in six bowel segments and higher water content in nine bowel segments. In conclusion, the majority of digesta dehydration occurs early in the proximal large bowel, while the greatest increases in viscosity occur in the distal bowel. Relatively small decreases in digesta water content result in large increases in digesta viscosity. Psyllium, and to a lesser extent polycarbophil, are able to resist dehydration, resulting in a softer digesta.