Amino acid supplementation does not alter whole-body phenylalanine kinetics in Arabian geldings

Kristine L. Urschel, Raymond J. Geor, Mark D. Hanigan, Pat A. Harris

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


Stable isotope infusion methods have not been extensively used in horses to study protein metabolism. The objectives were to develop infusion and sampling methodologies for [1-13C] phenylalanine and apply these methods to determine whether the addition of supplemental amino acids to a control diet affected whole-body phenylalanine kinetics in mature horses. Arabian geldings were studied using a 6-h primed (9 μmol/kg), constant (6 μmol kg-1 h-1) i.v. infusion of L-[1-13C] phenylalanine, with blood and breath sampled every 30 min, to measure whole-body phenylalanine kinetics in response to receiving the control diet (n = 12) or the control diet supplemented with equimolar amounts of glutamate (+Glu; 55 mg kg-1 d-1; n = 5), leucine (+Leu; 49 mg kg-1 d-1; n = 5), lysine (+Lys; 55 mg kg-1 d-1; n = 5), or phenylalanine (+Phe; 62 mg kg-1 d-1; n = 6). The plasma concentrations of the supplemented amino acid in horses receiving the +Leu, +Lys, and +Phe diets were 58, 53, and 36% greater, respectively, than for the control treatment (P < 0.05). Isotopic plateau was attained in blood [1-13C] phenylalanine and breath 13CO2 enrichments by 60 and 270 min, respectively. Phenylalanine flux (+20%) and oxidation (+110%) were greater (P < 0.05) in horses receiving the +Phe treatment than in those fed the control diet. There was no effect of treatment diet on nonoxidative phenylalanine disposal or phenylalanine release from protein breakdown. The developed methods are a valuable way to study protein metabolism and assess dietary amino acid adequacy in horses and will provide a useful tool for studying amino acid requirements in the future.

Original languageEnglish
Pages (from-to)461-469
Number of pages9
JournalJournal of Nutrition
Issue number3
StatePublished - Mar 1 2012

ASJC Scopus subject areas

  • Medicine (miscellaneous)
  • Nutrition and Dietetics


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