title: Effects of barley grain processing and dietary ruminally degradable protein on urea nitrogen recycling and nitrogen metabolism in growing lambs.
abstract: The objective of this study was to determine how interactions between dietary ruminally degradable protein (RDP) level and ruminally fermentable carbohydrate (RFC) alter urea N transfer to the gastrointestinal tract (GIT) and the utilization of this recycled urea N in rapidly growing lambs fed high-N diets. Four Suffolk ram lambs (34.8 +/- 0.5 kg of BW) were used in a 4 x 4 Latin square design with 21-d periods and a 2 x 2 factorial arrangement of dietary treatments. The dietary factors studied were 1) dry-rolled vs. pelleted barley as the principal source of RFC and 2) dietary levels of RDP of 60 vs. 70% (% of CP). All diets contained 28.8 g of N/kg of DM. Experimental diets were composed of 80% concentrate mixture and 20% barley silage (DM basis) and were fed twice daily at 0900 and 1700 as total mixed rations. Nitrogen balance was measured from d 15 to 20, and urea N kinetics were measured from d 15 to 19 using intrajugular infusions of [(15)N(15)N]-urea. Nitrogen intake (P = 0.001) and fecal (P = 0.002) and urinary (P = 0.03) N excretion increased as dietary RDP level increased, but the method of barley processing had no effect. Feeding dry-rolled compared with pelleted barley (P = 0.04) as well as feeding 60% RDP compared with 70% RDP (P = 0.04) resulted in a greater N digestibility. Whole-body N retention was unaffected (P >/= 0.74) by dietary treatment. Dietary treatment had no effect on endogenous production of urea N and its recycling to the GIT; however, across dietary treatments, endogenous production of urea N (45.8 to 50.9 g/d) exceeded N intake (42.3 to 47.9 g/d). Across dietary treatments, 30.6 to 38.5 g/d of urea N were recycled to the GIT, representing 0.67 to 0.74 of endogenous urea N production; however, 0.64 to 0.76 of urea N recycled to the GIT was returned to the ornithine cycle. In summary, although dietary treatment did not alter urea N kinetics, substantial amounts of hepatic urea N output were recycled to the GIT under the dietary conditions used in this study, and additional research is required to determine how this recycled urea N can be efficiently captured by bacteria within the GIT.
authors: Department of Animal and Poultry Science, University of Saskatchewan, Saskatoon, Canada.
authors: D
authors: D
authors: Kiran
authors: T
authors: T
authors: Mutsvangwa
mesh_terms: D000042:Absorption; D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D000831:Animals, Newborn; D001806:Blood Urea Nitrogen; D004040:Dietary Carbohydrates / Q000378:metabolism / Q000494:pharmacology; D004044:Dietary Proteins / Q000378:metabolism / Q000494:pharmacology*; D005243:Feces / Q000737:chemistry; D005285:Fermentation; D005511:Food Handling / Q000379:methods*; D001467:Hordeum; D009584:Nitrogen / Q000378:metabolism* / Q000493:pharmacokinetics / Q000652:urine; D009587:Nitrogen Isotopes; D011897:Random Allocation; D012417:Rumen / Q000378:metabolism* / Q000382:microbiology; D012756:Sheep / Q000254:growth & development / Q000378:metabolism; D013152:Splanchnic Circulation
chemical_list: D004040:Dietary Carbohydrates; D004044:Dietary Proteins; D009587:Nitrogen Isotopes; D009584:Nitrogen