Schmidt Bradie M, Gonda Michael G, MacNeil Michael D
Department of Animal Science, South Dakota State University, Brookings, SD.
Department of Animal, Wildlife and Grassland Sciences, University of the Free State, Bloemfontein, South Africa.
Transl Anim Sci. 2020 Sep 1;4(3):txaa162. doi: 10.1093/tas/txaa162. eCollection 2020 Jul.
Ultrasound technology provides cattle breeders with a quick, noninvasive, and inexpensive way to measure carcass data on live animals. Ultrasound data are used as indicator traits in cattle genetic evaluations for economically relevant carcass traits. Ultrasound cattle genetic evaluations assume homogeneous additive genetic and residual variance. Thus, the objective was to partition phenotypic variance in ultrasound carcass measurements into components for additive genetic effects, technicians, contemporary groups within technicians, and residual and to examine the homogeneity of these variances among image interpretation laboratories. Records of longissimus muscle area (LMA), percentage of intramuscular fat (IMF), and subcutaneous fat depth (SFD), measured using ultrasound, were provided by the American Angus Association ( = 65,967), American Hereford Association ( = 43,182), and American Simmental Association ( = 48,298). The data also included contemporary group, technician, imaging lab, and a three-generation pedigree for each animal. Variance components for ultrasound carcass measurements were first estimated with univariate animal models for each breed and imaging laboratory using derivative-free restricted maximum likelihood. Then, treating data from each imaging laboratory as separate traits, genetic correlations between laboratories for LMA, percentage of IMF, and subcutaneous fat were estimated with trivariate animal models. The technician explained 12-27%, 5-23%, and 4-26% of the variance for IMF, SFD, and LMA, respectively, across all three breeds. Variance due to technician was often greater than variance due to additive genetic effects but almost always less than that explained by the contemporary group. Within breeds, estimates of additive genetic variance for LMA, SFD, and IMF differed (range divided by mean) among laboratories by 4.5%, 21.5%, and 39.4 % (Angus); 31.6%, 15.0%, and 49.1% (Hereford); and 19.9%, 46.6%, and 55.3% (Simmental), respectively. Likewise, estimates of residual variance for LMA, SFD, and IMF differed among laboratories by 43.4%, 22.9%, and 43.3% (Angus); 24.9%, 15.2%, and 79.2% (Hereford); and 26.4%, 32.5%, and 46.2% (Simmental), respectively. Genetic correlations between labs across breeds ranged from 0.79 to 0.95 for IMF, 0.26 to 0.94 for SFD, and 0.78 to 0.98 for LMA. The impact of the observed heterogeneity of variance between labs on genetic evaluation requires further study.
超声技术为养牛户提供了一种快速、无创且经济的方法来测量活体动物的胴体数据。超声数据被用作牛遗传评估中与经济相关的胴体性状的指示性性状。超声牛遗传评估假定加性遗传方差和残差方差是同质的。因此，本研究的目的是将超声胴体测量的表型方差分解为加性遗传效应、技术人员、技术人员内的当代组以及残差等成分，并检验这些方差在图像解读实验室之间的同质性。美国安格斯协会（n = 65,967）、美国赫里福德协会（n = 43,182）和美国西门塔尔协会（n = 48,298）提供了使用超声测量的背最长肌面积（LMA）、肌内脂肪百分比（IMF）和皮下脂肪深度（SFD）的记录。数据还包括当代组、技术人员、成像实验室以及每只动物的三代系谱。首先使用无导数限制最大似然法，通过单变量动物模型对每个品种和成像实验室的超声胴体测量的方差成分进行估计。然后，将每个成像实验室的数据视为单独的性状，使用三变量动物模型估计LMA、IMF百分比和皮下脂肪在各实验室之间的遗传相关性。在所有三个品种中，技术人员分别解释了IMF、SFD和LMA方差的12 - 27%、5 - 23%和4 - 26%。技术人员引起的方差通常大于加性遗传效应引起的方差，但几乎总是小于当代组所解释的方差。在品种内，LMA、SFD和IMF的加性遗传方差估计值在各实验室之间的差异（范围除以均值）分别为4.5%、21.5%和39.4%（安格斯）；31.6%、15.0%和49.1%（赫里福德）；以及19.9%、46.6%和55.3%（西门塔尔）。同样，LMA、SFD和IMF的残差方差估计值在各实验室之间的差异分别为43.4%、22.9%和43.3%（安格斯）；24.9%、15.2%和79.2%（赫里福德）；以及26.4%、32.5%和46.2%（西门塔尔）。跨品种各实验室之间的遗传相关性，IMF为0.79至0.95，SFD为0.26至0.94，LMA为0.78至0.98。各实验室之间观察到的方差异质性对遗传评估的影响需要进一步研究。
