Graduate School of Agricultural Science, Tohoku University, Sendai, Miyagi 980-8572, Japan.
Maebashi Institute of Animal Science, Livestock Improvement Association of Japan, Inc., Maebashi 371-0121, Japan.
J Anim Sci. 2022 Sep 1;100(9). doi: 10.1093/jas/skac241.
The low heritability and moderate repeatability of semen production traits in beef and dairy bulls suggest that nonadditive genetic effects, such as dominance and epistatic effects, play an important role in semen production and should therefore be considered in genetic improvement programs. In this study, the repeatability of semen production traits in Japanese Black bulls (JB) as beef bulls and Holstein bulls (HOL) as dairy bulls was evaluated by considering additive and nonadditive genetic effects using the Illumina BovineSNP50 BeadChip. We also evaluated the advantage of using more complete models that include nonadditive genetic effects by comparing the rank of genotyped animals and the phenotype prediction ability of each model. In total, 65,463 records for 615 genotyped JB and 48,653 records for 845 genotyped HOL were used to estimate additive and nonadditive (dominance and epistatic) variance components for semen volume (VOL), sperm concentration (CON), sperm motility (MOT), MOT after freeze-thawing (aMOT), and sperm number (NUM). In the model including both additive and nonadditive genetic effects, the broad-sense heritability (0.17 to 0.43) was more than twice as high as the narrow-sense heritability (0.04 to 0.11) for all traits and breeds, and the differences between the broad-sense heritability and repeatability were very small for VOL, NUM, and CON in both breeds. A large proportion of permanent environmental variance was explained by epistatic variance. The epistatic variance as a proportion of total phenotypic variance was 0.07 to 0.33 for all traits and breeds. In addition, heterozygosity showed significant positive relationships with NUM, MOT, and aMOT in JB and NUM in HOL, when the heterozygosity rate was included as a covariate. In a comparison of models, the inclusion of nonadditive genetic effects resulted in a re-ranking of the top genotyped bulls for the additive effects. Adjusting for nonadditive genetic effects could be expected to produce a more accurate breeding value, even if the models have similar fitting. However, including nonadditive genetic effects did not improve the ability of any model to predict phenotypic values for any trait or breed compared with the predictive ability of a model that includes only additive effects. Consequently, although nonadditive genetic effects, especially epistatic effects, play an important role in semen production traits, they do not improve prediction accuracy in beef and dairy bulls.
精液生产性状在肉牛和奶牛公牛中的低遗传力和中等可重复性表明，非加性遗传效应，如显性和上位性效应，在精液生产中起着重要作用，因此应在遗传改良计划中考虑。本研究利用 Illumina BovineSNP50 BeadChip，通过考虑加性和非加性遗传效应，评估了日本黑牛（JB）作为肉牛和荷斯坦牛（HOL）作为奶牛公牛的精液生产性状的可重复性。我们还通过比较每个模型的基因型动物的等级和表型预测能力，评估了使用包含非加性遗传效应的更完整模型的优势。总共使用了 615 头已鉴定 JB 的 65463 个记录和 845 头已鉴定 HOL 的 48653 个记录，以估计精液量（VOL）、精子浓度（CON）、精子活力（MOT）、冻融后精子活力（aMOT）和精子数量（NUM）的加性和非加性（显性和上位性）方差分量。在包含加性和非加性遗传效应的模型中，所有性状和品种的广义遗传力（0.17 至 0.43）均高于狭义遗传力（0.04 至 0.11），且 VOL、NUM 和 CON 之间的广义遗传力和可重复性之间的差异非常小。多态性环境方差的很大一部分由上位性方差解释。所有性状和品种的上位性方差占总表型方差的比例为 0.07 至 0.33。此外，当包含杂合率作为协变量时，JB 中的杂合率与 NUM、MOT 和 aMOT 以及 HOL 中的 NUM 呈显著正相关。在模型比较中，非加性遗传效应的包含导致了对加性效应的顶级基因型公牛的重新排名。即使模型具有相似的拟合度，调整非加性遗传效应也有望产生更准确的育种值。然而，与仅包含加性效应的模型相比，包含非加性遗传效应并不能提高任何模型预测任何性状或品种的表型值的能力。因此，尽管非加性遗传效应，特别是上位性效应，在精液生产性状中起着重要作用，但它们并不能提高肉牛和奶牛公牛的预测准确性。
