Cerebrocortical necrosis in ruminants: an attempt to identify the source of thiaminase in affected animals.

We have calculated that the high thiaminase activity in the rumen of CCN-affected animals could degrade all the thiamine usually ingested and synthesized.We have confirmed that thiaminase-producing B. thiaminolyticus and Cl. sporogenes can be isolated from heat-treated rumen contents of CCN-affected sheep and cattle. The thiaminase from cultures of these bacteria is more active with the co-substrates pyridine, 3-picoline and pyridoxine than with aniline, whereas with the thiaminase from rumen fluid and faecal extracts the converse is true. The thiaminase of faecal extracts can use certain pyrrole and imidazole derivatives as co-substrates whereas the bacterial thiaminases cannot. There are also marked differences in membrane filtration, gel filtration, electrophoretic mobility and pH dependence. We conclude that neither B. thiaminolyticus nor Cl. sporogenes is the real source of rumen thiaminase.