Consumption of retrograded (RS3) but not uncooked (RS2) resistant starch shifts nitrogen excretion from urine to feces in cannulated piglets

To study the effect of resistant starch (RS) on the route of nitrogen excretion, we fed three groups of six cannulated piglets each a diet containing either uncooked resistant starch (RS2), retrograded resistant starch (RS3) or glucose. The use of piglets with a cannula at the end of the ileum allowed measurement of the amount of nitrogen that entered the colon. Ileal digesta, urine and feces were collected quantitatively and weighed, and dry matter, starch and nitrogen content were determined. We hypothesized that RS2 would lower colonic absorption of nitrogen when compared with RS3, because RS2 may be more fermentable than RS3, thus trapping more nitrogen in bacteria. The piglets fed RS3 had a significantly higher production of ileal digesta and feces than the piglets fed glucose or RS2. In the piglets fed RS2, 44% of the amount of RS fed was recovered in the ileal digesta; in the piglets fed RS3, 71% was recovered. Thus, more fermentable material entered the colon in the RS3-fed piglets than in the RS2-fed piglets. Virtually no starch was recovered in the feces of any dietary group, Replacement of glucose by either RS2 or RS3 did not affect nitrogen retention but increased fecal nitrogen excretion. Compared with glucose, RS3 but not RS2 reduced urinary nitrogen excretion, mainly in the form of urea, and reduced the amount of nitrogen absorbed by the colon when expressed as a percentage of the amount of nitrogen entering the colon. This study provides evidence that RS3, but not RS2, shifts nitrogen excretion from urine to feces in cannulated piglets.