Correlation matrix between the top 20 ruminal bacterial genera and rumen fermentation parameters (A) and between the top 20 ruminal bacterial genera and milk performance variables (B). Positive correlations are shown in red and negative correlations are shown in green. The color intensity is proportional to the correlation values [r] within a correlation group. * p < 0.05; ** p < 0.01. AN = ammonia nitrogen, AA = acetate, PA = propionate, IBA = isobutyrate, BA = butyrate, VA = valerate, IVA = isovalerate, VFA = total volatile fatty acids, AA_PA = the ratio of acetate to propionate, MY = milk yield, ECM = energy corrected milk, TS = total solids, MUN = milk urea nitrogen, SCC = somatic cell count.