Twenty-five strains of ruminococci were isolated from seven sheep fed chaffed lucerne hay, or mixtures of cereal chaff and lucerne chaff, for 18 months. Antiserum to each strain was produced in rabbits and used to classify the strains by cross-agglutination. Two main groups and a subgroup were identified which served to characterize half (12 of 25) of the strains isolated. Group 1 (7 strains) and the subgroup (2 strains) were all classified as Group 2 comprised 3 strains of An indirect fluorescent-antibody technique was also used to show antigenic relationships amongst the isolates. Fluorescence cross-reactions were obtained among 13 strains of using group 1 antisera. Similarly a group 2 antiserum labelled 7 of the 12 strains of isolated. The persistence of these serotypes in the rumen was demonstrated by the isolation of cross-agglutinating strains of from one animal at intervals throughout the experimental period. Recovery of cross-agglutinating strains of and from more than one animal suggests that a given serotype becomes disseminated among animals which are housed together. Furthermore, the isolation of group 1 and group 2 ruminococci from the same sheep indicates that the group-specific determinants were not dependent on the rumen environment for expression. It is concluded that selection was rigorous enough to maintain recognizably different genetic strains in the rumen against mutation pressure.


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