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Abstract
The resting level and vertical displacement during ruminoreticular contractions, of the cardia, reticulo-omasal orifice, ruminoreticular fold, cranial pillar (CP), dorsal and ventral coronary pillars, roof of the main dorsal rumen, floors of the reticulum, cranial sac of the rumen, main ventral rumen, and caudal dorsal blind sac were measured in 4 cows. The rumen was 56 cm deep and the cardia 22 cm ventral to the roof of the rumen. The CP exhibited the greatest vertical displacement during contractions (15 cm) of the structures examined. The CP partitioned digesta into cranial and caudal pools and was able to partially restrain cranial flow of digesta during B sequences (BS). The movement of the CP was examined in greater detail in cows of high and low susceptibility to bloat. Significant differences were observed between cows in resting level and vertical displacement of the CP, and some differences were correlated with differences in bloat susceptibility. Fewer BS contractions were evident in cows which were susceptible to bloat. We conclude that bloat susceptibility is not caused by differences between cows in the functional anatomy of the ruminoreticulum, but these differences may contribute to variations in the disorder.