Given that dysfunction in the intestinal microbiota leads to mastitis [6,7], and accounts for damaged AhR activation [15], as well as on the trail indicating a role for abnormal tryptophan metabolism in mastitis [29], we hypothesized that impairing the induction of AhR ligands by disrupting of the intestinal microbiota could contribute to mastitis development. This evidence concerns the gene AHR and mastitis.