Thiaminase I in the Development of Cerebrocortical Necrosis in Sheep and Cattle

MEMBERS of the B group of vitamins are synthesized by ruminal microflora1, and it has therefore been assumed2 that ruminants do not require thiamine in their diet. In Cerebrocortical necrosis of sheep and cattle3, however, tissue thiamine levels are low, resulting in cellular anoxia, characteristic damage to the cortical neurones3, raised blood keto-acids and lactate, and lowered transketolase4 activity. Moreover, plasma pyruvate kinase activity is elevated5, indicating a severe disturbance in carbohydrate metabolism. The decrease in thiamine levels was shown to result from the presence of a thiaminase in the ruminal contents of affected animals6,7, and we have since found this enzyme in all cases of cerebrocortical necrosis examined in this laboratory. It was present not only in the ruminal contents, but throughout the alimentary tract. We have now examined further the nature of this enzyme.