Production diseases of dairy cows include several pathologies and are considered manmade problems caused by the inability of cows to achieve a feed energy intake matching their high production requirements [1]. A correct management of production diseases demands early diagnostic and prognostic parameters, in order to implement the necessary adjustments in the management system and reduce the prevalence of clinical cases [2]. A previous study of our group had indicated that forestomachs walls express immune receptors and cytokines and the rumen liquor contains leukocytes able to produce IFN-γ [3]. Forestomach immune response could react to “dangers” arising within the forestomach environment, but also elsewhere in the body. Our working hypothesis implied that ruminal fluids could be an important source of diagnostic information for the identification of herds at risk for production diseases, in addition to the traditional analysis. We first demonstrated that the diet can influence the immune response in forestomachs. Diverse leukocyte populations at very low concentrations and IFN-γ were revealed in some samples of rumen fluids, with a clear inhibition of the response observed in all the animals fed the maize-supplemented diet, compared to a normal and a soy-supplemented diet. We better characterized the leukocytes subpopulations in the rumen liquor, isolating B cells, monocytes and γδ T cells. We also compared the leukocyte composition in ruminocentesis versus nasal probe sampling. We observed no significant statistical difference between samples collection techniques (p-value = 0.1). Finally we performed a field survey (146 cows from 13 farms) in order to find correlation among the immune profile of the rumen liquor (FACS and molecular analysis), blood, and faecal parameters. Clinically healthy animals showed a farm specific immunologic pattern of the rumen liquor: low CD45 mRNA expression (leukocytes), low or absent IFN-γ, few or absent B-cells. Whereas farms at risk for general wellness presented high levels of CD45 and IFN-γ, increased numbers of B-cells and other leukocyte populations. We can conclude that the epithelial cells of ruminant forestomachs can react to disturbances of the fermentation processes due to improper diets, and the inflammatory response can be sustained by infiltrating leukocytes. Our data points into the idea that dairy farms could be ranked according to a risk score using the inflammatory markers in rumen fluids, that could integrate the usual, consolidated information.