Department of Animal Science, University of Padova, Viale dell'Università 16, 35020 Legnaro, PD, Italy.
J Dairy Sci. 2011 Oct;94(10):5183-93. doi: 10.3168/jds.2011-4297.
The objective of this study was to estimate genetic parameters for milk protein fraction contents, milk protein composition, and milk coagulation properties (MCP). Contents of α(S1)-, α(S2)-, β-, γ-, and κ-casein (CN), β-lactoglobulin (β-LG), and α-lactalbumin (α-LA) were measured by reversed-phase HPLC in individual milk samples of 2,167 Simmental cows. Milk protein composition was measured as percentage of each CN fraction in CN (α(S1)-CN%, α(S2)-CN%, β-CN%, γ-CN%, and κ-CN%) and as percentage of β-LG in whey protein (β-LG%). Rennet clotting time (RCT) and curd firmness (a(30)) were measured by a computerized renneting meter. Heritabilities for contents of milk proteins ranged from 0.11 (α-LA) to 0.52 (κ-CN). Heritabilities for α(S1)-CN%, κ-CN%, and β-CN% were similar and ranged from 0.63 to 0.69, whereas heritability of α(S2)-CN%, γ-CN%, and β-LG% were 0.28, 0.18, and 0.34, respectively. Effects of CSN2-CSN3 haplotype and BLG genotype accounted for more than 80% of the genetic variance of α(S1)-CN%, β-CN%, and κ-CN% and 50% of the genetic variance of β-LG%. The genetic correlations among the contents of CN fractions and between CN and whey protein fractions contents were generally low. When the data were adjusted for milk protein gene effects, the magnitude of the genetic correlations among the contents of milk protein fractions markedly increased, indicating that they undergo a common regulation. The proportion of β-CN in CN correlated negatively with κ-CN% (r=-0.44). The genetic relationships between CN and whey protein composition were trivial. Low milk pH correlated with favorable MCP. Genetically, contents and proportions of α(S1)- and α(S2)-CN in CN were positively correlated with RCT. The relative proportion of β-CN in CN exhibited a genetic correlation with RCT of -0.26. Both the content and the relative proportion of κ-CN in CN did not correlate with RCT. Weak curds were genetically associated with increased proportions in CN of α(S1)- and α(S2)-CN, decreased contents of β-CN and κ-CN, and decreased proportion of κ-CN in CN. Negligible effects on the estimated correlations between a(30) and κ-CN contents or proportion in CN were observed when the model accounted for milk protein gene effects. Increasing β-CN and κ-CN contents and relative proportions in CN and decreasing the content and proportions of α(S1)-CN and α(S2)-CN and milk pH through selective breeding exert favorable effects on MCP.
本研究旨在估计牛奶蛋白分数含量、牛奶蛋白组成和牛奶凝固特性（MCP）的遗传参数。在 2167 头西门塔尔牛的个体牛奶样本中，通过反相高效液相色谱法测量 α(S1)-、α(S2)-、β-、γ-和 κ-酪蛋白（CN）、β-乳球蛋白（β-LG）和 α-乳白蛋白（α-LA）的含量。牛奶蛋白组成以 CN 中各 CN 分数的百分比（α(S1)-CN%、α(S2)-CN%、β-CN%、γ-CN%和 κ-CN%）和乳清蛋白中 β-LG 的百分比（β-LG%）来表示。凝乳酶凝固时间（RCT）和凝乳硬度（a(30)）通过计算机凝乳仪测量。乳蛋白含量的遗传力范围为 0.11（α-LA）至 0.52（κ-CN）。α(S1)-CN%、κ-CN%和 β-CN%的遗传力相似，范围为 0.63 至 0.69，而 α(S2)-CN%、γ-CN%和 β-LG%的遗传力分别为 0.28、0.18 和 0.34。CSN2-CSN3 单倍型和 BLG 基因型的效应解释了 α(S1)-CN%、β-CN%和 κ-CN%遗传变异的 80%以上和 β-LG%遗传变异的 50%。CN 分数含量之间以及 CN 与乳清蛋白分数含量之间的遗传相关性通常较低。当数据调整为牛奶蛋白基因效应时，牛奶蛋白分数含量之间的遗传相关性显著增加，表明它们受到共同调节。CN 中 CN 分数的比例与 κ-CN%呈负相关（r=-0.44）。CN 和乳清蛋白组成之间的遗传关系微不足道。低牛奶 pH 值与良好的 MCP 相关。遗传上，CN 中 α(S1)-和 α(S2)-CN 的含量和比例与 RCT 呈正相关。CN 中 β-CN 的相对比例与 RCT 呈-0.26 的遗传相关性。CN 中 κ-CN 的含量和相对比例均与 RCT 无关。弱凝乳与 CN 中 α(S1)-和 α(S2)-CN 的相对比例增加、β-CN 和 κ-CN 的含量减少以及 CN 中 κ-CN 的相对比例减少有关。当模型考虑牛奶蛋白基因效应时，对 a(30)与 CN 中 κ-CN 含量或比例之间的估计相关性几乎没有影响。通过选择性育种增加 CN 中 β-CN 和 κ-CN 的含量和相对比例，降低 α(S1)-CN 和 α(S2)-CN 的含量和比例以及牛奶 pH 值，对 MCP 产生有利影响。
