Activated immune responses of forestomachs might be associated with lower susceptibility to subacute ruminal acidosis (one of the metabolic ruminant disorders induced by high-concentrate diets), as evidenced by the higher expression of toll-like receptor 2 (TLR2) and toll-like receptor 4 (TLR4) in the rumen mucosal epithelium, compared to that in the mucosal epithelium of acidosis-susceptible cattle [49]. This evidence concerns the gene TLR4 and acidosis disorder.