Estimation of empty body water in steers by urea dilution

Urea dilution has been proposed as a practical method for estimating body composition in live cattle. The objectives of this study were to evaluate the urea dilution technique by comparing urea space to direct measurement of empty body water in steers and to develop prediction equations for empty body water in live steers using urea space parameters. Urea space was determined in 68 mixed-breed and 50 Angus steers ranging in live weight from 210 to 517 kg by the measurement of change in plasma urea nitrogen concentration before and 12 minutes after the midpoint of an intravenous infusion of 130 mg urea (20% solution w/v in 0.9% saline infused over 2 minutes) per kg live weight. Water in ground samples from carcass and digesta-free non-carcass fractions was determined by lyophilization. Linear relationships for pooled data of both groups of steers existed between empty body water and urea space (r = 0.96, P less than 0.001). Prediction of empty body water in live steers was improved by including live weight as an independent variable in a multiple regression equation (Sy X x = 7.2 kg for pooled data). Live weight alone predicted empty body water with a standard error of the estimate 36% larger than the multiple regression prediction using urea space and live weight.