title: Measurement of total body water content in horses, using deuterium oxide dilution.
abstract: OBJECTIVE
  To measure total body water (TBW) content in horses, using deuterium oxide (D2O) dilution.
  
  
  METHODS
  Six 8- to 10-year-old healthy untrained mixed-breed horses, weighing (mean +/-SD) 503.4 +/- 64.0 kg.
  
  
  METHODS
  After a 12-hour nonfeeding period, 6 horses were given D2O (0.14 g/kg of body weight) via nasogastric tube. Blood samples were collected from a preplaced indwelling jugular vein catheter prior to and 1 to 8, 10, 12, 14, and 24 hours after administration of D2O. Blood samples were centrifuged immediately, and plasma was collected and stored at -70 C until analysis. The D2O content in plasma was measured by zinc reduction to deuterium gas. The resulting gas was measured, using an isotope ratio mass spectrometer.
  
  
  RESULTS
  Deuterium oxide was rapidly absorbed from the gastrointestinal tract of all horses, and reached peak (mean +/- SD) plasma concentration (1,454.4 +/- 163 delta D/ml or parts/thousand) 1 hour after administration. Plasma concentration decreased slowly during the next 2 to 3 hours, then remained statistically constant from 2 to 5 hours (early plateau phase) and 3 to 7 hours (late plateau phase) after administration. Mean +/- SEM TBW content was 623.0 +/- 2.2 ml/kg (62.3% of body weight) for the early plateau phase and 630.3 +/- 2.2 ml/kg (63.0% of body weight) for the late plateau phase.
  
  
  CONCLUSIONS
  Deuterium oxide dilution appears to be of value for measurement of TBW content in horses, and has a 4-hour plateau effect. Equilibration of D2O with large intestinal water may be the reason for the prolonged equilibrium time and plateau effect seen in these horses.
  
  
  CONCLUSIONS
  Deuterium oxide appears safe and efficacious for determining TBW content in horses and may be helpful for determining changes in TBW content during exercise and disease.
authors.affiliation: Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville 37901-1071, USA.
authors.forename: F M
authors.initials: FM
authors.lastname: Andrews
authors.forename: J A
authors.initials: JA
authors.lastname: Nadeau
authors.forename: L
authors.initials: L
authors.lastname: Saabye
authors.forename: A M
authors.initials: AM
authors.lastname: Saxton
mesh_terms: D000818:Animals; D001823:Body Composition / Q000502:physiology*; D001834:Body Water; D001835:Body Weight / Q000502:physiology; D017666:Deuterium Oxide / Q000032:analysis* / Q000097:blood; D005260:Female; D006736:Horses / Q000097:blood / Q000502:physiology*; D008297:Male; D011865:Radioisotope Dilution Technique / Q000662:veterinary*; D012016:Reference Values; D012044:Regression Analysis; D013997:Time Factors; D015032:Zinc
chemical_list: D015032:Zinc; D017666:Deuterium Oxide