Evaluation of the use of deuterium oxide dilution techniques for determination of body composition of beef steers.

Body composition as estimated by a one- or two-compartment deuterium oxide dilution technique was compared with directly measured body composition of 15 large- and 15 small-frame steers. Body composition of the steers was measured at 219, 412 and 603 kg live weight. Empty body protein was overestimated (P less than .05) 3.6% from a one-compartment model (1 CM, using the slope, intercept method), while empty body protein was underestimated (P less than .05) 5.4% from a two-compartment kinetic model (2CM). Empty body ether extract estimated by 1 CM was not significantly different from the direct method, although 4.7% larger. Empty body ether extract was overestimated (P less than .001) 32.2% by the 2CM. Empty body water was accurately estimated from the 1CM when a 3.2% correction factor was used for the overestimation of total body water by the 1CM, but water in gastrointestinal tract contents was overestimated (P less than .001) 13.4% by the 1CM. Empty body water was underestimated (P less than .001) 7.8% by the 2CM, and water in gastrointestinal tract contents was overestimated (P less than .001) 41.8% by the 2CM due to its dependence on regression equations that differ between groups of cattle. The 2CM offered no advantage over the 1CM. A three-compartment model was not better than the 2CM in estimating body water compartments. Assuming the amount of empty body water associated with either empty body protein or ash to be constant seemed to be valid. Suggested values calculated from data presented in the literature for growing cattle with an empty body weight greater than 175 kg are .302 and .0668, respectively, for the ratios of protein and ash to water. The relationship between empty body fat and water was, percentage empty body fat = 94.27--(1.267)(percentage empty body water), which had a 1.25 residual standard deviation and a .98 coefficient of determination.