The effect of starch infusion at the distal ileum on urea recycling and bacterial nitrogen excretion

Six gilts, with an average BW of 70 kg, were fitted with a simple T-cannula at the distal ileum to study the effect of continuous starch infusion on urea kinetics by means of a radioisotope dilution technique. The pigs were fed twice daily 600 g of a cornstarch-based diet formulated to contain 16% CP by supplementation with isolated soy protein. Infusion of starch, compared with water, decreased (P < .05) plasma urea concentration, urea pool size, and entry, excretion, and degradation rates; urea turnover rate and urea space were not affected (P > .05). Expressed as a percentage of total entry rate, approximately 40% of urea was recycled into the digestive tract in both infusion treatments. The stimulation of microbial fermentation in the large intestine resulted in an increase (P < .05) in fecal N excretion, which was mainly due to an increased excretion of bacterial N. This increase could not be attributed to a greater secretion of urea into the large intestine and its subsequent utilization by the intestinal microflora. The increased bacterial N assimilation after starch infusion led to a reduction in ammonia absorption from the large intestine, which in turn was reflected by a reduced urinary N excretion. As a result, the overall N balance was not affected. In a second experiment, two barrows, with an average BW of 80 kg, were fed twice daily 1.4 kg of a cerealbased diet. The body urea pool of both pigs was labeled with a single injection of 1 g and 2 g of [15N]urea, respectively. Thereafter, feces were collected quantitatively for 120 h, and bacteria were isolated from feces. The highest concentration of [sup.15]N was measured in bacteria isolated from feces collected 24 to 48 h after injection. It was concluded that endogenous urea enters the large intestine via ileal digesta rather than by luminal secretion into the large intestine and may be utilized for bacterial N assimilation. Key Words: Pigs, Urea Recycling, Large Intestine, Fermentation
A study was done to determine the effects of starch infusion at the distal ileum on urea recycling and bacterial nitrogen excretion. Results of the study show that continuous infusion of starch stimulates microbial fermentation which decreases the amount of endogenous urea recycled in the gastrointestinal tract. Nitrogen balance is unaffected because ammonia is synthesized into bacterial protein and reduced urinary nitrogen excretion compensates for increased fecal nitrogen excretion.