Suppression of skin reactivity to bovine tuberculin in repeat tests

In cattle sensitised with killed Mycobacterium bovis an intradermal injection of either 0.3mg or 0.1mg bovine purified protein derivative tuberculin in the caudal fold suppressed skin reactivity to both bovine and avian tuberculin in comparative cervical tuberculin tests carried out 4 and 7 days later. Complete return to original sensitivity did not occur in all cattle when re-tested 60 days later but this level of sensitivity was not significantly different from that measured in initial tests. There were large individual variations in skin reaction to the sensitising dose in all treatment groups as found by others working with naturally infected cattle.