title: Amino acid utilization by the hindlimb of warmblood horses at rest and following low intensity exercise.
abstract: BACKGROUND
  In particular branched-chain amino acids might limit muscle protein loss in pathological conditions. Little is known on basic amino acid utilization of muscle in horses.
  
  
  OBJECTIVE
  To assess amino acid utilization by the hindlimb of horses at rest and following low intensity exercise. ANIMALS & METHODS: Amino acid uptake by the hindlimb was investigated using the arteriovenous difference technique. Blood from six warmblood mares (mean age 12 ± 3 (SD) years and weighing 538 ± 39 kg) was collected simultaneously from the (transverse) facial artery and from the caudal vena cava. Food was withheld for 12 hours prior to exercise. Exercise comprised a standardized treadmill protocol consisting of 5 minutes of walk, 20 minutes of trot, and thereafter another 5 minutes of walk. Amino acids were determined quantitatively by means of anion exchange chromatography. Statistical analysis was performed using a general linear mixed model.
  
  
  RESULTS
  Amino acids with the largest average extraction at rest were citrulline (11.1 ± 9%), cystine (8.3 ± 36%), serine (7.9 ± 11%), and leucine (5.9 ± 9%). Of the 25 amino acids studied, none showed a significant difference following exercise. Glycine (485 ± 65 μmol/L), glutamine (281 ± 40 μmol/L), valine (183 ± 26 μmol/L), and serine (165 ± 22 μmol/L) showed highest plasma concentrations. The average extraction for α-aminobutyric acid at rest was 18.2 ± 26%. Arterial plasma citrulline concentration was higher than venously.
  
  
  CONCLUSIONS
  Citrulline, cystine, serine, and leucine might be regarded as most important amino acids at rest in warmblood mares.
  
  
  CONCLUSIONS
  Further investigation is necessary into the specific role of leucine supplementation to preserve or restore body protein in horses.
authors.affiliation: Department of Equine Sciences, Medicine Section, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands.
authors.forename: L W E
authors.initials: LW
authors.lastname: Peters
authors.forename: E
authors.initials: E
authors.lastname: Smiet
authors.forename: M G M
authors.initials: MG
authors.lastname: de Sain-van der Velden
authors.forename: J H
authors.initials: JH
authors.lastname: van der Kolk
mesh_terms: D000596:Amino Acids / Q000097:blood* / Q000378:metabolism*; D000613:Aminobutyrates / Q000097:blood; D000818:Animals; D002852:Chromatography, Ion Exchange / Q000662:veterinary; D005260:Female; D006614:Hindlimb / Q000378:metabolism*; D006736:Horses / Q000502:physiology*; D010805:Physical Conditioning, Animal
chemical_list: D000596:Amino Acids; D000613:Aminobutyrates