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Nutrient Physiology, Metabolism, and Nutrient-Nutrient Interactions

Dietary and Endogenous Amino Acids Are the Main Contributors to Microbial Protein in the Upper Gut of Normally Nourished Pigs^1,2

³ Department of Animal and Poultry Science, University of Guelph, Guelph, Canada N1G 2W1; ⁴ Cargill Animal Nutrition Philippines Inc, Pulilan, Bulacan, Philippines; ⁵ Agriculture and Agri-Food Canada, Sherbrooke, J1M 1Z3 Canada; ⁶ I.N.R.A. UMR SENAH Centre de Recherches de Rennes, 35590 Saint Gilles, France; and ⁷ Department of Surgery, State University of New York, Stony Brook, NY 11794

Although amino acids (AA) synthesized by enteric microbiota in the upper gut of nonruminants can be absorbed, they do not necessarily make a net contribution to the host's AA supply. That depends on whether protein or nonprotein nitrogen sources are used for microbial protein production. We determined the contributions of urea, endogenous protein (EP), and dietary protein (DP) to microbial valine (M.VAL) at the distal ileum of growing pigs, based on isotope dilutions after a 4-d continuous infusion of L-[1-¹³C]valine to label EP and of [¹⁵N¹⁵N]urea. Eight barrows were assigned to either a cornstarch and soybean meal-based diet with or without 12% added fermentable fiber from pectin. Dietary pectin did not affect (P > 0.10) the contributions of the endogenous and DP to M.VAL. More than 92% of valine in microbial protein in the upper gut was derived from preformed AA from endogenous and DP, suggesting that de novo synthesis makes only a small contribution to microbial AA.

^* To whom correspondence should be addressed. E-mail: cdelange{at}uoguelph.ca.

Manuscript received 8 December 2008. Initial review completed 5 January 2009. Revision accepted 11 March 2009.

Published online 29 April 2009.