Fig. 6

Ordination of CAP analysis displaying the factors influencing rumen bacterial and viral communities. The CAP model with TDN, protein, and zinc as independent variables explained a significant portion of the variation in bacterial OTUs (P = 0.001, F = 2.736, variation explained = 33.9%, ANOVA permutation test for CAP) (a). Subsequent testing of the marginal effects of each term found TDN (P = 0.001, F = 4.342), zinc (P = 0.002, F = 3.587), and protein (P = 0.012, F = 2.379) to vary significantly with the microbial communities. Backward selection identified TDN, protein, zinc, and microbial functional diversity (Shannon’s diversity index) as potential drivers of rumen viral populations (b). The CAP model including these independent variables explained a significant portion of the variation in viral metagenomes (P = 0.002, F = 1.383, variation explained = 35.6%, ANOVA permutation test for CAP). Investigation of the marginal effects of each variable revealed TDN (P = 0.001, F = 1.936), zinc (P = 0.025, F = 1.482), and microbial functional diversity (P = 0.022, F = 1.402) to be the predominant factors influencing rumen viral populations. 27CDS—27% condensed distillers solubles; 40MDGS—40% modified distillers grains plus solubles; 55CS—55% corn silage