Effects of threonine supplementation on whole-body protein synthesis and plasma metabolites in growing and mature horses

S. L. Mastellar, A. Moffet, P. A. Harris, K. L. Urschel

Research output: Contribution to journalArticlepeer-review

5 Scopus citations


Current equine threonine requirement estimates do not account for probable use of threonine to maintain gut health and mucin synthesis. The objective of this study was to determine if threonine supplementation (+Thr) would increase whole-body protein synthesis (WBPS) in weanling colts (Study 1) and adult mares (Study 2). Both studies used a crossover design, where each of six animals was studied twice while receiving the isonitrogenous diets. The basal diets contained lower threonine levels (Basal) than the threonine (+Thr) supplemented diets. Threonine intakes in mg/kg BW/day were as follows: 79 (Basal) and 162 (+Thr) for Study 1 and 58 (Basal) and 119 (+Thr) for Study 2, in comparison to the NRC estimated requirements of 81 and 33 mg/kg BW/day for weanling and mature horses, respectively.Following 5 days of adaptation, blood samples were taken before and 90 min after the morning concentrate meal. The next day, whole-body phenylalanine kinetics were determined using a 2 h primed, constant infusion of [13C]sodium bicarbonate followed by a 4 h primed, constant infusion of [1-13C]phenylalanine. Most plasma amino acid (AA) concentrations were elevated post-feeding (P < 0.01). Lysine and valine plasma concentrations were lower (P < 0.10), while methionine, threonine, and glycine plasma concentrations were greater (P < 0.10) 90 min post concentrate meal feeding with +Thr in both studies. Phenylalanine flux, intake, oxidation and non-oxidative disposal were similar between treatments (P > 0.05). These findings suggest that supplementation of a single AA can affect the metabolism of several AAs and threonine was not a limiting AA in these diets.

Original languageEnglish
Pages (from-to)147-153
Number of pages7
JournalVeterinary Journal
StatePublished - Jan 1 2016

Bibliographical note

Funding Information:
The information reported in this paper is part of a project of the Kentucky Agricultural Experiment Station (15-07-009) and is published with the approval of the Director. The portion of the project involving the weanlings was funded by the WALTHAM-Buckeye Foundation . The portion of the project involving adult mares was supported by Agriculture and Food Research Initiative Competitive Grant no. 2012-67015-19448 from the USDA National Institute of Food and Agriculture . Tammy Brewster-Barnes contributed technical expertise helping with sampling and sample analyses. Preliminary results of this project were presented as abstracts at the 2013 Equine Science Society meeting and the 2014 ADSA ASAS Joint Annual Meeting.

Publisher Copyright:
© 2015 Elsevier Ltd.


  • Amino acids
  • Horse
  • Phenylalanine kinetics
  • Protein synthesis
  • Threonine

ASJC Scopus subject areas

  • Animal Science and Zoology
  • Veterinary (all)


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