Cow mature weight (MWT) is heritable and affects the costs and efficiency of a breeding operation. Cow weight is also influenced by the environment, and the relationship between the size and profitability of a cow varies depending on production system. Producers, therefore, need tools to incorporate MWT in their selection of cattle breeds and herd replacements. The objective of this study was to estimate breed and heterotic effects for MWT using weight-age data on crossbred cows. Cow’s MWT at 6 yr was predicted from the estimated parameter values—asymptotic weight and maturation constant (k)—from the fit of the Brody function to their individual data. Values were obtained for 5,156 crossbred cows from the U.S. Meat Animal Research Center (USMARC) Germplasm Evaluation Program using 108,957 weight records collected from approximately weaning up to 6 yr of age. The cows were produced from crosses among 18 beef breeds. A bivariate animal model was fitted to the MWT and k obtained for each cow. The fixed effects were birth year-season contemporary group and covariates of direct and maternal breed fractions, direct and maternal heterosis, and age at final weighing. The random effects were direct additive and residual. A maternal additive random effect was also fitted for k. In a separate analysis from that used to estimate breed effects and (co)variances, cow MWT was regressed on sire yearling weight (YWT) Expected Progeny Differences by its addition as a covariate to the animal model fitted for MWT. That regression coefficient was then used to adjust breed solutions for sire selection in the USMARC herd. Direct heterosis was 15.3 ± 2.6 kg for MWT and 0.000118 ± 0.000029 d−1 for k. Maternal heterosis was −5.7 ± 3.0 kg for MWT and 0.000130 ± 0.000035 d−1 for k. Direct additive heritabilities were 0.56 ± 0.03 for MWT and 0.23 ± 0.03 for k. The maternal additive heritability for k was 0.11 ± 0.02. The direct additive correlation between MWT and k was negligible (0.08 ± 0.09). Adjusted for sire sampling, Angus was heaviest at maturity of the breeds compared. Deviations from Angus ranged from −8.9 kg (Charolais) to −136.7 kg (Braunvieh). Ordered by decreasing MWT, the breeds ranked Angus, Charolais, Hereford, Brahman, Salers, Santa Gertrudis, Simmental, Maine Anjou, Limousin, Red Angus, Brangus, Chiangus, Shorthorn, Gelbvieh, Beefmaster, and Braunvieh. These breed effects for MWT can inform breeding programs where cow size is considered a key component of the overall profitability.

中文翻译：

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品种和杂种优势对肉牛成熟体重的影响


奶牛成熟体重 (MWT) 具有遗传性，会影响育种操作的成本和效率。奶牛的体重也受到环境的影响，奶牛的体型和盈利能力之间的关系因生产系统而异。因此，生产者需要工具将 MWT 纳入牛品种和牛群替代品的选择中。本研究的目的是利用杂交奶牛的体重年龄数据来估计 MWT 的品种和杂种优势效应。奶牛 6 年的 MWT 是根据布罗迪函数与个体数据的拟合估计参数值（渐近体重和成熟常数 (k)）预测的。使用从大约断奶至 6 岁期间收集的 108,957 份体重记录，从美国肉类动物研究中心 (USMARC) 种质评估计划中获得了 5,156 头杂交奶牛的值。这些奶牛是由 18 个肉牛品种杂交产生的。将双变量动物模型拟合到 MWT 并获得每头牛的 k。固定效应是出生年份-季节当代群体以及直接和母本品种分数、直接和母本杂种优势以及最终称重年龄的协变量。随机效应是直接累加效应和残差效应。 k 还拟合了母体加性随机效应。在用于估计品种效应和（共）方差的单独分析中，通过将奶牛 MWT 作为协变量添加到适合 MWT 的动物模型中，对公牛一岁体重 (YWT) 预期后代差异进行回归。然后使用该回归系数来调整 USMARC 牛群中父系选择的品种解决方案。 MWT 的直接杂种优势为 15.3 ± 2.6 kg，k 的直接杂种优势为 0.000118 ± 0.000029 d−1。 MWT 的母本杂种优势为-5.7 ± 3.0 kg，k 的母本杂种优势为0.000130 ± 0.000035 d−1。 MWT 的直接累加遗传力为 0.56 ± 0.03，k 的直接累加遗传力为 0.23 ± 0.03。 k 的母体加性遗传力为 0.11 ± 0.02。 MWT 和 k 之间的直接加性相关性可以忽略不计 (0.08 ± 0.09)。根据父本取样进行调整后，安格斯在成熟时的品种中体重最重。与安格斯牛的偏差范围为 -8.9 kg（夏洛莱牛）至 -136.7 kg（布劳恩牛）。按 MWT 递减排序，这些品种排名为安格斯、夏洛莱、赫里福德、婆罗门、塞勒斯、圣格特鲁迪斯、西门塔尔、缅因安茹、利木赞、红安格斯、布朗格斯、Chiangus、短角、Gelbvieh、Beefmaster 和 Braunvieh。 MWT 的这些品种效应可以为育种计划提供信息，其中奶牛大小被认为是整体盈利能力的关键组成部分。