Direct and Indirect Measurement of Total Body Water in the Growing Beagle 1

Summary

Total body water (TBW) was measured by tritium and desiccation in 43 beagles between 0.2 and 13 kg body weight. With desiccation, TBW increased at a single rate of 0.521 liters/kg body weight while with tritium there were two rates of increase, 0.738 liters/kg between a body weight of 0.2 and 3.5 kg and 0.552 liters/kg above a body weight of 3.5 kg. Above 3.5 kg, tritium measured a mean volume 1 liter larger than desiccation (p<.001). The TBW measured by tritium was 84% of the body weight at birth and decreased at a rate of 2.6%/kg, while with desiccation the TBW was 68% at birth and decreased at a rate of 2.0%/kg. The rate of decrease between methods was not statistically different; the mean difference between them was 13.8% (p<.001). On a fat-free wet weight basis there was no significant difference between the rates of decrease, but tritium measured a 15.6% larger volume than desiccation (p<.001).