Group A: present in all mammals examined. Important role in calf and piglet diarrhoea; role in lambs & foal diarrhoea less certain; not associated with diarrhoea in cats & dogs.

Groups B to E cause diarrhoea experimentally but importance in natural disease unknown.

Group B: pigs, sheep, cattle, rats, man. Group C: pigs, man, ferrets Group D: avian species Group E: pigs.

RVs from different animal species thought of as distinct but some transmission between species may occur naturally.