Evaluation of Urea Dilution as an Estimator of Body Composition in Mature Cows

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Abstract
The urea dilution technique was evaluated as an estimator of body composition in 40 nonpregnant cows. The cows ranged from 3 to 16 yr of age and included 29 beef type (28 Angus and Angus crossbreds and one Hereford) and 11 dairy type (Holstein). The percentage urea space was calculated using either live weight (LW) or empty body weight (EBW). Urea space was compared with carcass fat estimated from carcass specific gravity and from chemical composition of the 9-10-11th rib section. Coefficients of determination for estimating percentage fat calculated from carcass specific gravity using area space (LW) were .35 and .17 for the beef and dairy types, respectively, and .50 and .28 using urea space (EBW). The coefficients of determination for estimation of chemical composition using urea space (LW) were .36 and .09 and using urea space (EBW) were .64 and .41 for the beef and dairy types, respectively. Specific gravity of the -10-11th rid section was correlated to chemical composition (r2 = .86). Live weight was correlated to chemical composition (r2 = .47 and .27 for beef and dairy types, respectively). Including change in plasma urea-nitrogen (PUN) as an additional factor in a multiple regression with live weight improved the estimation of chemical composition (r2 = .66 and .62 for beef and dairy, respectively). Including initial PUN as a third factor in the regression equation increased the estimate of chemical composition in the dairy, but not in the beef type. The results indicate that the urea dilution technique can be a useful estimator of body composition between groups of mature cows. Copyright © 1983. American Society of Animal Science . Copyright 1983 by American Society of Animal Science

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