Validation of predictive equations for use of deuterium oxide dilution to determine body composition of dogs

Objective - To validate equations predicting body composition of dogs, using deuterium oxide dilution. Animals - 38 female and 37 male dogs selected by defined body weight and body condition criteria. Procedure - Measured equilibrated deuterium concentration in serum after IV administration of isotope was used to determine isotope space and predict body water, fat, nitrogen, and ash contents determined from analysis of homogenized carcass. Equations predicting body composition were derived, using regression analysis, and were validated, using data-splitting techniques. Results - Deuterium space (in kilograms) overestimated kilograms of body water content by mean 21.8% ± SD of 4.18%. Regression equations were derived and validated to predict kilograms of body water and ash from kilograms of deuterium space, and proportions of body water, fat, nitrogen, and ash from proportion of deuterium space. Coefficients of determination (r²) and means of standard errors of estimating new values (SEE) were, respectively, 0.993 and 0.4 kg for body water content, and 0.942 and 0.08 kg for ash content. For proportions, SEE were 2.0, 2.7, 0.1, and 0.4% for body water, fat, nitrogen, and ash, respectively. Two factors, time for isotope equilibration and whether samples were processed by vacuum sublimation, improved SEE for proportion of body water from 2.0 to 1.3% and of fat from 2.7 to 1.8%. Equations predicting absolute quantities of fat and nitrogen could be derived but not validated. Conclusions - Deuterium dilution can be used to predict body composition of dogs with precision equal to that determined for other species.