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This Article Free Via Open Access Full Text Full Text (PDF) All Versions of this Article: jas.2007-0039v1 86/3/660    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Marini, J. C. Articles by Murphy, M. R. PubMed PubMed Citation Articles by Marini, J. C. Articles by Murphy, M. R.

Nitrogen transactions along the gastrointestinal tract of cattle: A meta-analytical approach^1,2

J. C. Marini^*,3, D. G. Fox and M. R. Murphy

^* US Department of Agriculture/ARS Children’s Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston 77030; and Department of Animal Science, Cornell University, Ithaca, NY 14853; and and Department of Animal Science, University of Illinois, Urbana 61801

³ Corresponding author: marini{at}bcm.edu

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.

Key Words: cattle • endogenous • meta-analysis • nitrogen • requirement