The degree of stratification in the reticulorumen contents is considered a major explanatory factor for other morphological and physiological differences between ruminant feeding types. However, information on reticulorumen (RR) contents is usually gathered from dead animals or indirect such as passage kinetics. We hypothesized that, although the contents of the gastrointestinal tract can usually not be evaluated by ultrasonography, the three typical layers of stratified RR contents (gas dome, fibre mat, fluid) can be demonstrated by this technique. In three domestic cows, the gas dome in the cows' rumens could be demonstrated sonographically by reverberation lines running in parallel to the line demarcating the rumen mucosa, as is typical for the sonographic image of large, gas-filled spaces. More ventrally, the area behind the rumen mucosa showed typical pattern indicating gaseous inclusions, corresponding to the fibre mat inside the rumen. Further ventrally, in two of the animals, the area behind the demarcation line appeared dark without reverberation lines, as is typical for large fluid-filled spaces. When the technique was applied to a captive, habituated, browse-fed moose, no gas dome could be demonstrated, supporting the hypothesis that the reticulorumen contents of browsers are less stratified. The results of this study indicate that sonography represents a useful tool for the demonstration of RR contents stratification in live animal
