Reflux of (15)N-labeled uric acid after intracloacal infusion in broiler chickens fed low- or high-protein diets

Reflux of urine from the cloaca into the ceca provides chickens with a mechanism for recycling of urinary-Nitrogen (N) in a way analogous to urea recycling in mammals. However, it is unknown if reflux has substantial relevance in current poultry husbandry, where birds are fed ad libitum and have high protein intake. To evaluate the fate of urinary-N in ad libitum-fed broiler chickens, 15-day-old broilers were assigned to a high (21.9% CP, n = 22) or low (10.2 % CP, n = 22) protein diet. At 25 d of age, 20 broilers per dietary treatment were infused into the cloaca with a pulse dose of 107 mg [1,3-(15)N]-uric acid. N-contents and (15)N-enrichment in digesta, blood plasma, and body tissues were measured at 5, 30, 60, 90, 150, 300, 450, 600, 1,200, or 1,800 min after administration (n = 2 /time-point /diet). Two broilers per dietary treatment were infused with saline and served as control to analyze background (15)N-enrichment. The average total recovery (% of infused (w/w)) of (15)N from infused uric acid in all body tissues was low (2.9 ± 0.62 %), of which the largest proportion was found in carcass tissue (2.5 ± 0.60%). (15)N-enrichment was greatest in intestinal tissues. Even at 1,200 min, (15)N-enrichment of ceca (0.46 ± 0.169 APE) and colon (0.13 ± 0.159 APE) digesta was considerably exceeding background enrichment. (15)N-enrichment in excess of background enrichment in cecum and colon digesta (10-fold, P < 0.05), and (15)N recovery in intestinal tissues (4-fold, P < 0.01) were greater in birds fed the low protein diet compared with the high protein diet, speculatively pointing out differences in the occurrence of reflux, incorporation of uric acid-N derivatives in intestinal tissues by first-pass metabolism, and a prolonged digesta retention time in protein deficient birds. In conclusion, these data confirm that uric acid-N infused in the cloaca can be refluxed and used for body N-deposition, but its contribution to whole body protein metabolism in broilers is probably limited.