Fig. 4

Differentially expressed metabolites in the rumen fluid, serum, milk and urine of the lactating dairy cows identified by partial least squares discriminant analysis (PLS). The colored boxes on the right indicate the relative concentrations of the corresponding metabolite in each biofluid. R: rumen fluid; M: milk; S: serum; U: urine. Darker green indicates a lower relative concentration and darker red represents a higher relative concentration. The x-axis represents the first principal component of the PLS (variable importance projection, VIP value), and the blue dots represent the different metabolites