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reticulo-omasal stenosis, ruminal acidosis and alkalosis, microbial inactivity, putrefaction and peritonitis [3]. ately measure the rumen and the dimensions of the in-gesta layers [5,6], this imaging technique is limited to the examination of the head and legs in mature cattle because of the disproportion between the size of the equipment and the size of the patient [7]. In contrast, * Correspondence: ubraun@vetclinics.uzh.chmat in the middle and a dorsal gas cap.mat was marked by the abrupt cessation of the reverberation artifacts. It was not possible to differentiate a fibre mat and a ventral fluid phase. The rumen could be imaged from the right side in 21 cows (47%). Conclusions: Ultrasonography is well suited for the detailed examination of the rumen of cows. The reference values obtained from this study add to the diagnostic tools that are available for the assessment of bovine patients. Background The rumen of adult cattle occupies most of the left hemiabdomen and extends across the ventral midline into the right hemiabdomen caudoventrally [1]. The an-terior dorsal blind sac, separated from the dorsal sac o