A procedure for extracting rotaviral double-stranded ribonucleic acid (RNA) directly from fecal and intestinal specimens collected from calves and pigs is described. This procedure provides a rapid, simple, reproducible method of obtaining rotaviral double-stranded RNA preparations suitable for electrophoretic analysis in polyacrylamide-agarose composite gels. The rotaviral genome electrophoretic migration pattern produced by double-stranded RNA extracted directly from a specimen by this procedure was qualitatively identical to the electrophoretic migration pattern obtained with double-stranded RNA extracted from purified rotavirus derived from the same specimen. Direct extraction of specimens containing porcine rotavirus-like virus by this procedure gave preparations that had electrophoretic migration patterns similar, but not identical, to the characteristic electrophoretic migration pattern of the rotaviral genome. Sufficient rotaviral double-stranded RNA could be extracted from 6 ml of fecal or intestinal specimen by this procedure to permit 15 or more electrophoretic assays.

A group A rotavirus (ID isolate) recovered from a diarrheic beef calf possessed a short genome electropherotype. This short genome electropherotype was a stable characteristic of the ID isolate as it remained unchanged through 3 passages in gnotobiotic calves or through 19 passages in MA104 cell cultures. Subgroup analysis with monoclonal antibodies in an enzyme-linked immunosorbent assay established that the isolate was a subgroup 1 rotavirus. Neutralization tests demonstrated that this isolate was a distinct serotype from the human group A rotavirus S2 isolate (short genome electropherotype) and the turkey group A rotavirus 174 isolate (semi-short genome electropherotype). The ID isolate was pathogenic for 5-to 21-day-old gnotobiotic calves, inducing diarrhea within 48 h postinoculation.

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The genome electropherotyping technique was used to examine group A rotaviral infections of diarrheic calves ranging from 1 to 85 days of age in 2 beef and 27 dairy herds. Coelectrophoresis studies demonstrated 38 distinct bovine group A rotavirus genome electropherotypes; all were long genome electropherotypes, and none had extra segments or unusual segment rearrangements. Genome electropherotypes in fecal specimens from diarrheic calves previously inoculated orally with a commercial, modified-live group A rotavirus vaccine differed from the vaccine genome electropherotype. Generally, when fecal specimens for genome electropherotyping were collected from two or more different calves within the same herd over a relatively short time, only one genome electropherotype was detected within a given herd. Different genome electropherotypes were detected in the same herd, however, when fecal specimens were obtained from different diarrheic calves over longer intervals (6 months or more). Twenty-three group A rotavirus strains with distinct genome electropherotypes, from diarrheic calves in 22 herds, were isolated and plaque purified in cell culture, and all were subgroup 1 group A rotaviruses. Non-group A rotavirus genome electropherotypes were not detected in 131 fecal specimens, negative for group A rotavirus, collected from diarrheic calves in 17 dairy herds.

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