Phenotypic and genetic analysis of milk and serum element concentrations in dairy cows

摘要

Enhancing micronutrient (i.e., mineral and vitamin)concentrations within milk and serum from dairy cowsis important for both the health of the cow and the nutritivevalue of the milk for human consumption. However,a good understanding of the genetics underlyingthe micronutrient content in dairy cattle is needed tofacilitate such enhancements through feeding or breedingpractices. In this study, milk (n = 950) and serum(n = 766) samples were collected from Holstein-Friesiandairy cows (n = 479) on 19 occasions over a 59-moperiod and analyzed for concentrations of importantelements. Additionally, a subset of 256 milk sampleswas analyzed for concentrations of vitamin B_(12). Cowsbelonged to 2 genetic lines (average and highest geneticmerit for milk fat plus protein yield) and wereassigned to 1 of 2 diets based on either a by-productor homegrown ration. Univariate models accountingfor repeated records were used to analyze element andvitamin B_(12) data and investigate the effect of genotypeand feeding system as well as derive estimates of variancecomponents and genetic parameters. Bivariatemodels were used to study correlations both withinand between milk and serum. Only concentrations ofHg in milk were seen to be affected by genotype, withhigher concentrations in cows with high genetic merit.In contrast, element concentrations were influenced byfeeding system such that cows fed the homegrown diethad increased milk concentrations of Ca, Cu, I, Mn,Mo, P, and K and increased serum concentrations ofCd, Cu, Fe, Mo, and V. Cows on the by-product diethad increased milk concentrations of Mg, Se, and Naand increased serum concentrations of P and Se. Heritability(h~2) estimates were obtained for 6 milk and 4serum elements, including Mg (h~2_(milk) = 0.30), K (h~2_(serum)= 0.18), Ca (h~2_(milk) = 0.20; h~2_(serum) = 0.12), Mn (h~2_(milk) = 0.14), Cu (h~2_(serum) = 0.22), Zn (h~2_(milk) = 0.24), Se (h~2_(milk) = 0.15; h~2_(serum) = 0.10), and Mo (h~2_(milk) = 0.19). Significantestimates of repeatability were observed in all milk andserum quantity elements (Na, Mg, P, K, and Ca) aswell as 5 milk and 7 serum trace elements. Only K inmilk and serum was found to have a significant positivegenetic and phenotypic correlation (0.52 and 0.22,respectively). Significant phenotypic associations werenoted between milk and serum Ca (0.17), Mo (0.19), andNa (−0.79). Additional multivariate analyses betweenmeasures within sample type (i.e., milk or serum) revealedsignificant positive associations, both phenotypicand genetic, between some of the elements. In milk, Sewas genetically correlated with Ca (0.63), Mg (0.59),Mn (0.40), P (0.53), and Zn (0.52), whereas in serum,V showed strong genetic associations with Cd (0.71),Ca (0.53), Mn (0.63), Mo (0.57), P (0.42), K (0.45),and Hg (−0.44). These results provide evidence thatelement concentrations in milk and blood of dairy cowsare significantly influenced by both diet and geneticsand demonstrate the potential for genetic selection anddietary manipulation to alter nutrient concentration toimprove both cow health and the healthfulness of milkfor human consumption.