Genetic Background of Micellar and Soluble Calcium and Phosphorus Predicted From Bovine Milk Mid-infrared Spectra
Abstract BackgroundMid-infrared spectroscopy (MIRS) is a valuable tool to determine milk composition and quality, and to collect data at population level. In milk, Ca and P are partitioned between micellar (MP) and soluble phase (SP), both with important effects on milk coagulation properties; in particular, greater mineral content in MP translates into better milk coagulation ability. Nevertheless, the high analytic costs of gold standard quantification 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 mid-infrared spectra of 111,653 individual milk samples from 9,519 Italian Holstein cows. Sources of non-genetic variation for MP and SP of Ca and P were investigated, and their genetic associations with milk yield, quality and coagulation properties were estimated.ResultsThe MP of Ca and P decreased with parity but increased along the lactation, resembling the trend of protein content. Both MP and SP of Ca and P showed exploitable genetic variation and were heritable, and they were associated with traits of interest for the dairy industry, in particular milk yield and protein content. Furthermore, negative correlations between the two phases of the same mineral were estimated. The MP was negatively related to milk yield.ConclusionsThe MP and SP of the same mineral are negatively correlated, meaning that it is possible to improve mineral partition toward MP, in order to get milk with better technological properties. The current selection index of Italian Holstein breed gives positive emphasis on milk protein (content and yield) and thus it is indirectly improving the MP of Ca and P while reducing their SP content. Future research will focus on the genomic architecture of such traits to evaluate the role of potential specific genes in the determination of these mineral fractions in cow milk.