Colonic compensation in transmissible gastroenteritis of swine.
Absorption of water and electrolytes by the small and large intestine was examined using a nonabsorbable marker technique in 3-day-old and 3-wk-old pigs. One-half of the pigs in each group were orally infected with transmissible gastroenteritis virus; the remaining pigs served as controls. Three-day-old control pigs concentrated the nonabsorbable fluid marker twelve fold along the small and large intestine, indicating an efficiency of about 95% in absorption of the exogenous daily fluid load presented to the intestine. In contrast, the marker concentration in infected pigs showed no change whatsoever along either the small or large intestine, indicating a complete absence of net fluid absorption or secretion in these animals. Three-week-old control pigs concentrated the marker similarly to the 3-day-old group, with the bulk of the fluid absorption occurring in the small intestine. Infected pigs in the 3-wk-old group had marked net fluid secretion in the proximal small intestine, so that about twice the fluid load was presented to the large intestine of the 3-wk-old infected pigs as compared to the 3-day-old infected group. However, in contrast to the 3-day-old infected group, the large intestine of the 3-wk-old infected pigs increased fluid absorption some six times over the control, and this compensatory response prevented diarrhea in these older animals. Analysis of luminal contents indicated that in the older pigs, unabsorbed carbohydrate was almost completely fermented to short-chain fatty acids in the colon, whereas in the younger pigs the carbohydrate passed through the colon unchanged. These results demonstrate that development of microbial digestion, together with rapid short-chain fatty acid absorption, is a primary feature responsible for the colonic compensation in the older pigs with transmissible gastroenteritis.