The use of urea as a marker of body water in the nursing foal.

Urea, compared with deuterium oxide (D2O) as a reference, was used as a body marker to estimate body water volume in ten 2-month old nursing foals. Plasma urea clearance was regular over 10 h and the R2 of the disappearance curve was between 0.93 and 0.98. Mean urea space was about 4% lower than D2O space, but the standard deviation of the proportion of water in body weight was higher with urea (3.8%) than with D2O (1.6%). Calculated urea entry rate was 49 mg/h/kg LW0.75.