Abstract

In bovine milk, Ca and P are partitioned between micellar (MP) and soluble phase (SP), both having important effects on coagulation properties. In particular, greater mineral content in the MP translates into better milk coagulation ability. Nevertheless, the high analytic costs of gold standard methods hamper the possibility to deepen partition of minerals in MP and SP on a large scale. In this study, MP and SP of Ca and P were predicted from 111,653 milk mid-infrared spectra of Holstein cows to investigate genetic parameters. The average coefficient of determination of the prediction models in cross validation was 0.73. Heritability estimates of MP and SP of Ca and P ranged from 0.472 to 0.548 and the two phases of the same mineral were negatively correlated. The MP of Ca was genetically associated with protein yield (0.284) and content (0.658); in the case of MP of P, the latter were equal to 0.262 and 0.808, respectively. The current selection index of Italian Holstein places positive emphasis on protein percentage and yield, thus it is likely that the MP of the investigated minerals is increasing at the expense of the SP. In perspective, it would be important to assess genetic correlations between measured and predicted phenotypes to corroborate the use of such predictions for management and breeding purposes.

• Highlights

• Micellar and soluble fractions of Ca and P predicted from milk spectra are heritable.

• Micellar fraction of Ca and P is favourably genetically associated with traits of interest for the dairy industry, such as milk protein and coagulation properties.

• The Italian Holstein selection index emphasises protein percentage and yield, and thus it is indirectly improving micellar phase of Ca and P.

摘要

在牛乳中，Ca和P在胶束（MP）和可溶相（SP）之间分配，两者均对凝结特性产生重要影响。特别是，MP中较高的矿物质含量可转化为更好的牛奶凝结能力。然而，金标准方法的高分析成本阻碍了大范围深化MP和SP中矿物分配的可能性。在这项研究中，从荷斯坦奶牛的111,653头牛奶中红外光谱预测了Ca和P的MP和SP，以研究遗传参数。交叉验证中预测模型的平均确定系数为0.73。Ca和P的MP和SP的遗传度估计值在0.472至0.548之间，并且同一矿物的两相呈负相关。Ca的MP与蛋白产量（0.284）和含量（0.658）遗传相关。对于P的MP，后者分别等于0.262和0.808。意大利荷尔斯泰因州目前的选择指数积极强调蛋白质的百分比和产量，因此被调查矿物质的MP可能以SP为代价而增加。从角度来看，评估测得的表型和预测的表型之间的遗传相关性非常重要，以确证将这些预测用于管理和育种目的。

• 强调

• 从牛奶光谱预测的钙和磷的胶束和可溶部分是可遗传的。

• Ca和P的胶束级分与乳业感兴趣的性状遗传相关，例如乳蛋白和凝结特性。

• 意大利荷斯坦的选择指数强调蛋白质的百分比和产量，因此间接改善了钙和磷的胶束相。