Evaluation of the deuterium dilution method to estimate body composition in the barnacle goose: Accuracy and minimum equilibration time

We examined body composition in barnacle geese (Branta leucopsis) by proximate carcass analysis and by deuterium isotope dilution. We studied the effect of isotope equilibration time on the accuracy of total body water (TBW) estimates and evaluated models to predict fat-free mass (FFM) and fat mass (FM) from different measurements varying in their level of invasiveness. Deuterium enrichment determined at 45, 90, and 180 min after isotope injection did not differ significantly. At all sampling intervals, isotope dilution spaces (TBWd) consistently overestimated body water determined by carcass analysis (TBWc). However, variance in the deviation from actual TBW was higher at the 45-min sampling interval, whereas variability was the same at 90 and 180 min, indicating that 90 min is sufficient time to allow for adequate equilibration. At 90 min equilibration time, deuterium isotope dilution overestimated TBWc by 7.1% +/- 2.6% (P < 0.001, paired t-test, n = 20). This overestimate was consistent over the range of TBW studied, and TBWc could thus be predicted from TBWd (r(2) = 0.976, P < 0.001). Variation in TBWc and TBWd explained, respectively, 99% and 98% of the variation in FFM. FM could be predicted with a relative error of ca. 10% from TBW estimates in combination with body mass (BM). In contrast, BM and external body measurements allowed only poor prediction. Abdominal fat fresh mass was highly correlated to total FM and, if the carcass is available, allows simple means of fat prediction without dissecting the entire specimen.