Department of Animal Sciences, University of Wisconsin-Madison, Madison, WI, USA.
J Dairy Res. 2012 Feb;79(1):47-52. doi: 10.1017/S0022029911000744. Epub 2011 Oct 13.
Concomitant with intensive selection for increased milk yield, reproductive performance of dairy cows has declined in the last decades, in part due to an unfavourable genetic relationship between these traits. Given that the six main milk protein genes (i.e. whey proteins and caseins) are directly involved in milk production and hence have been a target of the strong selection aimed at improving milk yield in dairy cattle, we hypothesized that these genes could show selection footprints associated with fertility traits. In this study, we used an in-vitro fertilization (IVF) system to test genetic association between 66 single nucleotide polymorphisms (SNPs) in the four caseins (αS1-casein, αS2-casein, β-casein and κ-casein) and the two whey protein genes (α-lactalbumin and β-lactoglobulin) with fertilization rate and early embryonic development in the Holstein breed. A total of 6893 in-vitro fertilizations were performed and a total of 4661 IVF embryos were produced using oocytes from 399 ovaries and semen samples from 12 bulls. Associations between SNPs and fertility traits were analysed using a mixed linear model with genotype as fixed effect and ovary and bull as random effects. A multiple testing correction approach was used to account for the correlation between SNPs due to linkage disequilibrium. After correction, polymorphisms in the LALBA and LGB genes showed significant associations with fertilization success and blastocyst rate. No significant associations were detected between SNPs located in the casein region and IVF fertility traits. Although the molecular mechanisms underlying the association between whey protein genes and fertility have not yet been characterized, this study provides the first evidence of association between these genes and fertility traits. Furthermore, these results could shed light on the antagonistic relationship that exists between milk yield and fertility in dairy cattle.
伴随着对产奶量增加的强化选择，奶牛的繁殖性能在过去几十年中下降了，部分原因是这些性状之间存在不利的遗传关系。鉴于这六个主要的乳蛋白基因（即乳清蛋白和酪蛋白）直接参与产奶，因此一直是旨在提高奶牛产奶量的强烈选择的目标，我们假设这些基因可能显示与繁殖力性状相关的选择痕迹。在这项研究中，我们使用体外受精（IVF）系统来测试四个酪蛋白（αS1-酪蛋白、αS2-酪蛋白、β-酪蛋白和κ-酪蛋白）和两个乳清蛋白基因（α-乳白蛋白和β-乳球蛋白）中的 66 个单核苷酸多态性（SNP）与荷斯坦品种的受精率和早期胚胎发育之间的遗传关联。总共进行了 6893 次体外受精，使用来自 399 个卵巢的卵母细胞和来自 12 头公牛的精液样本生产了总共 4661 个 IVF 胚胎。使用混合线性模型，将基因型作为固定效应，卵巢和公牛作为随机效应，分析 SNP 与繁殖力性状之间的关联。使用多重测试校正方法来考虑由于连锁不平衡导致的 SNP 之间的相关性。校正后，LALBA 和 LGB 基因中的多态性与受精成功率和囊胚率显著相关。位于酪蛋白区域的 SNP 与 IVF 繁殖力性状之间未检测到显著关联。虽然乳清蛋白基因与繁殖力之间关联的分子机制尚未得到阐明，但本研究首次提供了这些基因与繁殖力性状之间关联的证据。此外，这些结果可能揭示了奶牛产奶量和繁殖力之间存在拮抗关系。
