Genomic information allows for a more accurate calculation of relationships among animals than the pedigree information, leading to an increase in accuracy of breeding values. Here, we used pedigree-based and single-step genomic approaches to estimate variance components and breeding values for β-hydroxybutyrate milk content (BHB). Additionally, we performed a genome-wide association study (GWAS) to depict its genetic architecture. BHB concentrations within the first 90 days of lactation, estimated from milk medium infrared spectra, were available for 30,461 cows (70,984 records). Genotypes at 42,152 loci were available for 9,123 animals. Low heritabilities were found for BHB using pedigree-based (0.09 ± 0.01) and genomic (0.10 ± 0.01) approaches. Genetic correlation between BHB and milk traits ranged from −0.27 ± 0.06 (BHB and protein percentage) to 0.13 ± 0.07 (BHB and fat-to-protein ratio) using pedigree and from −0.26 ± 0.05 (BHB and protein percentage) to 0.13 ± 0.06 (BHB and fat-to-protein ratio) using genomics. Breeding values were validated for 344 genotyped cows using linear regression method. The genomic EBV (GEBV) had greater accuracy (0.51 vs. 0.45) and regression coefficient (0.98 vs. 0.95) compared to EBV. The correlation between two subsequent evaluations, without and with phenotypes for validation cows, was 0.85 for GEBV and 0.82 for EBV. Predictive ability (correlation between (G)EBV and adjusted phenotypes) was greater when genomic information was used (0.38) than in the pedigree-based approach (0.31). Validation statistics in the pairwise two-trait models (milk yield, fat and protein percentage, urea, fat/protein ratio, lactose and logarithmic transformation of somatic cells count) were very similar to the ones highlighted for the single-trait model. The GWAS allowed discovering four significant markers located on BTA20 (57.5–58.2 Mb), where the ANKH gene is mapped. This gene has been associated with lactose, alpha-lactalbumin and BHB. Results of this study confirmed the usefulness of genomic information to provide more accurate variance components and breeding values, and important insights about the genomic determination of BHB milk content.

中文翻译：

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西门塔尔奶牛泌乳早期β-羟基丁酸的研究：遗传参数和基因组预测

与谱系信息相比，基因组信息可以更准确地计算动物之间的关系，从而提高育种值的准确性。在这里，我们使用基于谱系的单步基因组方法来估计 β-羟基丁酸乳含量 (BHB) 的方差分量和育种值。此外，我们还进行了全基因组关联研究（GWAS）来描述其遗传结构。根据牛奶介质红外光谱估算，泌乳期前 90 天内的 BHB 浓度可用于 30,461 头奶牛（70,984 条记录）。9,123 只动物的 42,152 个基因座的基因型可用。使用基于谱系 (0.09 ± 0.01) 和基因组 (0.10 ± 0.01) 的方法发现 BHB 遗传力较低。使用谱系，BHB 和牛奶性状之间的遗传相关性范围为 -0.27 ± 0.06（BHB 和蛋白质百分比）至 0.13 ± 0.07（BHB 和脂肪与蛋白质比率），并且范围为 -0.26 ± 0.05（BHB 和蛋白质百分比）至 0.13 ±使用基因组学得出 0.06（BHB 和脂肪与蛋白质的比率）。使用线性回归方法对 344 头基因型奶牛的育种值进行了验证。与 EBV 相比，基因组 EBV (GEBV) 具有更高的准确性（0.51 vs. 0.45）和回归系数（0.98 vs. 0.95）。对于验证奶牛，没有和有表型的两次后续评估之间的相关性，GEBV 为 0.85，EBV 为 0.82。使用基因组信息时的预测能力（(G)EBV 与调整表型之间的相关性） (0.38) 比基于谱系的方法 (0.31) 更高。成对双性状模型中的验证统计数据（产奶量、脂肪和蛋白质百分比、尿素、脂肪/蛋白质比率、乳糖和体细胞计数的对数变换）与单性状模型中突出显示的验证统计数据非常相似。GWAS 发现了位于ANKH基因定位的 BTA20 (57.5–58.2 Mb) 上的四个重要标记。该基因与乳糖、α-乳清蛋白和 BHB 相关。这项研究的结果证实了基因组信息在提供更准确的方差分量和育种值方面的有用性，以及有关 BHB 牛奶含量基因组测定的重要见解。