Effects of repeated urea dilution measurement on feedlot performance and consistency of estimated body composition in steers of different breed types.

Steers (20 Bos indicus cross [BIX] and 20 Bos taurus cross [BTX]) were randomly assigned to a 2x2 factorial experiment within two weight blocks per treatment 1) to study the effects of repeated urea dilution (UD) measurement on feedlot performance and 2) to determine the consistency of estimated body composition in steers of different breed types. Weights were taken on d 0, 42, 84, 126, and 140. Urea dilution was determined on half of the pens in the experiment, and ultrasonic measurement of backfat (BF) was performed on all cattle on d 0, 42, 84, and 126. Pen means of all performance variables were used in the analysis of variance. Carcass data were analyzed on an individual basis. Within periods, ADG was inconsistent between controls and steers on which UD was determined (1.95 vs 2.03, 1.61 vs 1.28, 1.51 vs 1.71, and 1.77 vs 1.47 kg, P = .23, .02, .09, and .11, respectively, for Periods 1, 2, 3, and 4, SEM = .07). Overall, UD had no effect (control vs UD, respectively) on ADG (1.70 vs 1.68 kg, P = .77, SEM = .07), DMI (8.26 vs 8.03 kg, P = .69, SEM = .36), gain efficiency (207 vs 209 g BW gain/kg DMI, P = .78, SEM = 2.34), hot carcass weight (HCWT; 360 vs 358 kg, P = .90, SEM = 2.52), or percentage of estimated carcass fat, (ECF; 38.8 vs 37.0%, P = .61, SEM = 1.05). Breed types (BIX vs BTX, respectively) had similar ADG (1.74 vs 1.64 kg, P = .27, SEM = .14), DMI (7.96 vs 8.30 kg, P = .50, SEM = .36), backfat thickness (16.4 vs 15.0 mm, P = .30, SEM = .45), and ECF (38.9% vs 36.6%, P = .48, SEM = 2.01). Urea dilution estimated empty body fat values increased with days on feed (14.4+/-1.36; 22.7+/-1.47; 26.0+/-1.36; 30.4+/-1.47%, respectively, for d 0, 42, 84, and 126). Using yield grade factors to calculate ECF consistently produced a value that was higher than empty body fat determined by UD (UDEBF) 14 d prior to slaughter (36.9+/-1.73 vs 30.4%+/-0.17). Significant correlation coefficients were found for the pooled data between UDEBF vs BF, r = .84; UDEBF vs live weight, r = .99; UDEBF vs ECF, r = .82; and UDEBF vs percentage of carcass protein, r = -.99. This study demonstrated that there are no detrimental effects of the urea dilution procedure on performance characteristics of feedlot cattle. Beef cattle of different breed types may be accurately evaluated with urea dilution.