Long-term consumption of high concentrate diet causes the accumulation of organic acid and a depression of pH values in rumen.When rumen pH decreased below 5.6 at least 3 hours one day, subacute ruminal acidosis (SARA) occurs.In the condition of SARA, free LPS released from gram-negative pathogens translocated into the circulatory system across the epithelial barrier of the gastrointestinal tract, thus initiating systemic inflammatory responses and host innate immune responses.