title: Nitrogen transactions along the gastrointestinal tract of cattle: A meta-analytical approach.
abstract: In ruminant animals, endogenous N (EN) secretions contribute to meeting the N requirement of the ruminal microflora. The EN also constitutes a sizable portion of the duodenal N flow, which might be available to the host animal. Most measures of EN have been accomplished with highly invasive techniques or unusual semisynthetic diets. By utilizing a statistical approach and data obtained from studies reporting duodenal, ileal, and fecal N flows in cattle, the EN losses and true digestibility of N were estimated for different segments of the gastrointestinal tract of cattle. A simulation for a reference diet (24.2 g of N/kg of OM, 32% NDF and carbohydrates of medium fermentation rate) consumed at 2% of BW daily estimated that the minimal contribution of EN to the N available in the rumen was 39%. The free EN represented 13% of the duodenal N flow, and when bacterial N of EN origin was considered, EN contributed 35% of the total N flow. The minimal entry of EN into various segments of the gastrointestinal tract was also estimated as: foregut, 10.54; small intestine, 3.10; and hindgut, 5.0 g/kg of OMI. Rumen dietary N degradability was 0.68, and true N digestibilities in the small intestine and hindgut were 0.75 and 0.49, respectively. A better understanding of the factors involved in EN losses will allow for a more accurate estimation of both N supply and N requirements. This will translate into improved accuracy of diet formulation and less N excreted into the environment.
authors: US Department of Agriculture/ARS Children's Nutrition Research Center, Houston 77030, USA. marini@bcm.edu
authors: J C
authors: JC
authors: Marini
authors: D G
authors: DG
authors: Fox
authors: M R
authors: MR
authors: Murphy
mesh_terms: D000818:Animals; D001419:Bacteria / Q000737:chemistry / Q000254:growth & development; D002417:Cattle / Q000378:metabolism*; D004032:Diet / Q000662:veterinary; D004063:Digestion / Q000502:physiology*; D005260:Female; D041981:Gastrointestinal Tract / Q000378:metabolism* / Q000382:microbiology; D008297:Male; D008954:Models, Biological; D009584:Nitrogen / Q000378:metabolism*; D012044:Regression Analysis
chemical_list: D009584:Nitrogen