Multivariate modelling of milk fatty acid profile to discriminate the forages in dairy cows' ration

Abstract

Although there are many studies on the importance of fatty acids (FA) in our diet and on the influence of dairy diets on FA metabolism, only a few investigate their predictive capacity to discriminate the type, amount and conservation method of farm forages. This research quantifies differences in milk FA concentrations and, using a supervised factorial discriminant analysis, assesses potential biomarkers when replacing maize with other silages, grass/lucerne hays or fresh grass. The statistical modelling identified three main clusters of milk FA profiles associated with silages, hays and fresh grass as dominant roughages. The main implication of a dairy cow feeding system based on poliphytic forages from permanent meadows is enhancing milk's nutritional quality due to an increase in beneficial omega-3 polyunsaturated FA, conjugated linoleic acids and odd chain FA, compared to feeding maize silage. The study also identified a small but powerful and reliable pool of milk FA that can act as biomarkers to authenticate feeding systems: C16:1 c-9, C17:0, C18:0, C18:3 c-9, c-12, c-15, C18:1 c-9, C18:1 t-11 and C20:0.

Figure 1

FDA scatterplot of the milk samples according to the five feeding groups based on the fatty acid profiles. The main function F1 (along x-axis) and F2 (along y-axis) accounted for 59.0% and 20.1% of the total variance, respectively. The 0.95 confidence ellipses are drawn around each centroid of groupings. High maize silage (HMS): blue dotted line and blue upward triangles; medium maize silage (MMS): red dotted-pointed line and red diamond symbols; mixed crop silages (MCS): solid purple line and purple closed circles; grass and lucerne hays (HAY): orange dotted line and orange plus symbols; green grass (GRG): green pointed line and green closed squares. The black arrows indicate the most significant (p < 0.05) discriminative FA that had correlation coefficient values higher than 0.20 with at least either F1 or F2 (for graphic purposes these significant correlations coefficients were multiplied 10 times according to the maximum value of F1 and F2).

Figure 2

Box–Whisker plots of fatty acids (g/100 g of total fatty acids) according to the five feeding groups. HMS, high maize silage; MMS, medium maize silage; MCS, mixed crop silages; HAY, grass and lucerne hays; GRG, green grass. The box plots represent the following descriptive statistics: median (bar in box), mean (+, red cross), 25% (Q1) and 75% (Q3) quartile (bottom and top end of the box), minimum [Q1 − 1.5 × (Q3 − Q1)] and maximum [Q1 + 1.5 × (Q3 − Q1)] whiskers (lines outside), minimum and maximum values (•, full black circles), outliers with a distance to box of 1.5–3.0 times interquartile range (°, empty circles) or higher than 3 times interquartile range (*, asterisks). For the fatty acids abbreviations see Table 3.