Spontaneous in vitro contractile activity of specimens from the abomasal wall of healthy cows and comparison among dairy breeds

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Abstract
Objective—To characterize and compare in vitro contractility patterns of sections of abomasal wall harvested from cattle of 3 dairy breeds. Sample Population—Longitudinal and circular smooth muscle preparations harvested from the antrum and body of the abomasum of 30 recently slaughtered Holstein-Friesian, Brown Swiss, and Simmental X Red Holstein cows. Procedure—Spontaneous isometric contractions of specimens in tissue baths of modified Krebs solution were recorded during a 4-hour period. Maximal amplitude, frequency of contractions, and change of basal tension were used to characterize contractility. Statistical analyses were used to test for differences among time periods, among breeds, between specimen locations, and between fiber orientations. Results—Myoactivity patterns of abomasal smooth muscle preparations are highly variable and differ on the basis of location and fiber orientation. Frequency of contractions differed significantly among time periods for longitudinally oriented specimens with decreasing frequencies of contractions over time. Maximal amplitude of the longitudinally oriented specimens from the antrum increased significantly, whereas maximal amplitude of the circularly oriented specimens from the antrum decreased significantly. Values did not differ significantly among breeds. Conclusions and Clinical Relevance—Patterns of spontaneous contractility of abomasal wall specimens are not homogeneous. During a 4-hour recording period, maximal amplitude and frequency of contractions of specimens varied significantly with respect to orientation and location; however, spontaneous contractile myoactivity did not differ significantly among breeds. Therefore, breed predisposition for displaced abomasum is not correlated with spontaneous activity of smooth muscle specimens. (Am J Vet Res 2002;63:1687–1694)