Rule D C, Arnold R N, Hentges E J, Beitz D C
J Anim Sci. 1986 Dec;63(6):1935-48. doi: 10.2527/jas1986.6361935x.
Urea dilution equations for prediction of empty body water in live cattle, developed by three separate groups of investigators, were evaluated by comparing empty body water calculated by these equations with that measured chemically in 6-, 12- and 18-mo-old crossbred beef steers (n = 10, 9 and 9, respectively). Of four equations for prediction of percent empty body water, one derived from mixed-breeds of steers overestimated empty body water in the 6-mo-old steers by 7.59% (P less than .05). For the 12- and 18-mo-old steers, calculated and measured percent empty body water did not differ (P greater than .05). Of seven equations for calculation of empty body water volume, two derived from Angus steers with an without live weight in the equation, and one derived from a combination of Angus and mixed-breeds of steers overestimated empty body water (P less than .05) in the 6-mo-old steers. No differences (P greater than .05) between calculated and measured empty body water volume were observed for either the 12- or 18-mo-old steers. When calculated empty body water values were regressed against that measured directly, all regression slopes were not different from 1 (P greater than .05). Intercepts from regressions involving percent empty body water (four equations) were not different from 0. Three of the seven equations for calculation of empty body water volume, one derived from bulls and the others from Angus steers had intercept estimates not different (P greater than .05) from 0. Validity required that these regressions have slopes not different from 1 and intercepts not different from 0. Empty body water calculated from equations that combined live weight and urea space were more highly correlated with directly measured empty body water than that calculated from equations derived only from urea space. Urea space correlations with body composition of our steers also were improved when live weight was included with urea space in multiple regression models. Results of this study suggest that before using any prediction equation for calculating body composition of cattle in vivo, equations should be tested with a sub-sample of cattle from the population for which its use is intended.
由三组不同的研究人员开发的用于预测活牛空体水分的尿素稀释方程，通过将这些方程计算出的空体水分与6、12和18月龄杂交肉牛（分别为n = 10、9和9头）化学测量的空体水分进行比较来评估。在四个预测空体水分百分比的方程中，一个源自阉牛杂交品种的方程高估了6月龄阉牛的空体水分7.59%（P < 0.05）。对于12和18月龄的阉牛，计算出的和测量的空体水分百分比没有差异（P > 0.05）。在七个计算空体水分体积的方程中，两个源自安格斯阉牛且方程中有无活重的方程，以及一个源自安格斯和阉牛杂交品种组合的方程高估了6月龄阉牛的空体水分（P < 0.05）。对于12或18月龄的阉牛，计算出的和测量的空体水分体积没有差异（P > 0.05）。当将计算出的空体水分值与直接测量的值进行回归分析时，所有回归斜率与1没有差异（P > 0.05）。涉及空体水分百分比（四个方程）的回归截距与0没有差异。七个计算空体水分体积的方程中有三个，一个源自公牛，其他源自安格斯阉牛，其截距估计与0没有差异（P > 0.05）。有效性要求这些回归的斜率与1没有差异且截距与0没有差异。与仅从尿素空间推导的方程计算出的空体水分相比，结合活重和尿素空间的方程计算出的空体水分与直接测量的空体水分相关性更高。当在多元回归模型中将活重与尿素空间一起纳入时，我们阉牛的尿素空间与身体组成的相关性也得到了改善。本研究结果表明，在使用任何预测方程计算牛体内身体组成之前，应使用目标群体中的一小部分牛对该方程进行测试。
