Use of Urea and Deuterium Oxide to Measure Body Composition'

The use of dilution of urea or deuterium oxide ( D 2 0 ) to estimate body water in cattle, sheep and pigs is reviewed. After equilibration, which requires about 20 min after infusion of urea and 4 to 6 h after infusion of D 2 0 , urea and D , 0 space estimated from dilution in water of blood are each closely related to total body water. Calculation of body composition from total body water can vary depending upon fill of the digestive tract. Dilution of urea or D 2 0 in water of blood before equilibration is related to empty body water, but there is too much variation in predictive equations from different groups of animals to apply any one equation to independent sets of data. The use of multicompartmental models more accurately describes the dilution of D 2 0 in water from blood after infusion of labeled water, but has not significantly improved estimates of body composition in all experiments. {