Department of Animal Science, University of Nebraska - Lincoln, Lincoln, NE.
USDA, ARS, Roman L. Hruska U.S. Meat Animal Research Center, Clay Center, NE.
J Anim Sci. 2019 Apr 3;97(4):1523-1533. doi: 10.1093/jas/skz045.
Cow mature weight (MWT) has increased in the past 30 yr. Larger cows cost more to maintain, but their efficiency-and thus profitability-depends on the production environment. Incorporating MWT effectively into selection and mating decisions requires understanding of growth to maturity. The objective of this study was to describe growth to maturity in crossbred beef cattle using Brody, spline, and quadratic functions. Parameter estimates utilized data on crossbred cows from cycle VII and continuous sampling phases of the Germplasm Evaluation Program at the U.S. Meat Animal Research Center. The MWT were estimated at 6 yr from the fitted parameters obtained from the Brody (BMWT), spline (SMWT), and quadratic (QMWT) functions. These were defined as BMWT, SMWT, and QMWT for the Brody, spline, and quadratic functions, respectively. Key parameters from the Brody function were BMWT and maturing constant. The spline was fitted as piecewise linear where the two linear functions joined at a knot. Key parameters were knot position and SMWT. For the quadratic model, the main parameter considered was QMWT. Data were scaled for fitting such that 180 d was the y-intercept with the average weight at 180 d (214.3 kg) subtracted from all weights. Weights were re-expressed by adding 214.3 kg after analysis. Once data were edited, with outliers removed, there were parameter estimates for 5,156, 5,041, and 4,905 cows for the Brody, spline, and quadratic functions, respectively. The average maturing constant (SD) was 0.0023 d-1 (0.0008 d-1). The mean MWT estimates (SD) from the Brody, spline, and quadratic functions were 650.0 kg (64.0 kg), 707.3 kg (79.8 kg), and 597.8 kg (116.7 kg), respectively. The spline function had the highest average R2 value when fit to individual cows' data. However, the Brody function produced more consistent MWT estimates regardless of the timeframe of data available and produced the fewest extreme MWT. For the spline and quadratic functions, weights through 4 and 5 yr of age, respectively, were needed before consistent estimates of MWT were obtained. Of the three functions fitted, the Brody was best suited for estimating MWT at a later age in crossbred beef cattle.
过去 30 年来，奶牛的成熟体重（MWT）一直在增加。更大的奶牛维持成本更高，但它们的效率——因此盈利能力——取决于生产环境。要有效地将 MWT 纳入选择和配种决策中，需要了解成熟过程中的生长情况。本研究的目的是使用 Brody、样条和二次函数来描述杂交肉牛的成熟过程。参数估计利用了美国肉类动物研究中心种质评估计划第七周期和连续采样阶段杂交奶牛的数据。从 Brody（BMWT）、样条（SMWT）和二次（QMWT）函数获得的拟合参数估计了 6 年的 MWT。这些分别定义为 Brody、样条和二次函数的 BMWT、SMWT 和 QMWT。Brody 函数的关键参数是 BMWT 和成熟常数。样条函数被拟合为分段线性，两条线性函数在一个节点处连接。关键参数是节点位置和 SMWT。对于二次模型，主要考虑的参数是 QMWT。数据进行了缩放拟合，使得 180 天是 y 截距，所有体重都减去了 180 天的平均体重（214.3 千克）。分析后，体重通过加上 214.3 千克重新表示。一旦编辑了数据，删除了异常值，Brody、样条和二次函数分别有 5156、5041 和 4905 头奶牛的参数估计。平均成熟常数（SD）为 0.0023 d-1（0.0008 d-1）。Brody、样条和二次函数的平均 MWT 估计值（SD）分别为 650.0 kg（64.0 kg）、707.3 kg（79.8 kg）和 597.8 kg（116.7 kg）。当拟合个别奶牛的数据时，样条函数的平均 R2 值最高。然而，Brody 函数无论可用数据的时间范围如何，都能产生更一致的 MWT 估计值，并且产生的极端 MWT 最少。对于样条和二次函数，分别需要在 4 岁和 5 岁之前的体重数据，才能获得一致的 MWT 估计值。在拟合的三个函数中，Brody 最适合在杂交肉牛的后期年龄估计 MWT。
