Changes in the rumen microbial community composition of dairy cows subjected to an acidogenic diet

In modern breeding systems, cows are subjected to many stress factors. Animals fed a high-grain diet may have a decreased rumen pH, which would lead to subacute ruminal acidosis syndrome. The aim of this study was to investigate the evolution of microbial community composition in cows undergoing a dietary stress challenge. Twelve cows were subjected to a challenge period that consisted of a rapid change of ration, from a normal (45.4:54.6 forage:concentrate) to a high-grain content diet (24.8:75.2 forage:concentrate) to induce subacute ruminal acidosis. Individual rumen fluid content samples were collected before (T0) and during the challenge (T3, T14, T28). The DNA from rumen contents was extracted, purified, and sequenced to evaluate bacterial populations, and sequencing was performed on Illumina MiSeq. The effect of animal conditions on rumen microbial community was quantified through a linear mixed model. The acidogenic diet created 2 main clusters: ruminal hypomotility (RH) and milk fat depression (MFD). The microbial composition did not differ in T0 between the 2 groups, whereas during the challenge Ruminococcus spp., Treponema spp., Methanobrevibacter spp., and Methanosphaera spp. concentrations increased in RH cows; and Succinivibrio spp. and Butyrivibrio spp. concentrations increased in MFD cows. Prevotella spp. and Ruminococcus spp. were negatively correlated, whereas the Christenellaceae family was positively correlated with both Methanobrevibacter spp. and Methanosphaera spp. Moreover, the same diet affected cows' microbiota composition differently, underlying the impact of the host effect. Other studies are necessary to deepen the relationship between microbiota composition and host.