Bovine anaplasmosis: elimination of the carrier state with injectable long-acting oxytetracycline.

Long-acting oxytetracycline was administered intramuscularly (20 mg/kg) at 3-day intervals to each of 16 naturally infected Anaplasma marginale carrier beef cows; 8 of the 16 cows were given 3 injections and the other 8 cows were given 4 injections. Four cows seropositive for A marginale served as untreated controls. Rapid card agglutination and complement fixation tests were performed 5 times during the 130-day posttreatment period. All treated cows became negative to both serologic procedures, whereas control cows remained seropositive. Three splenectomized calves that received pooled blood from the treated cows, 120 days following treatment, remained free of anaplasmosis for 60 days following inoculation. One splenectomized calf that received blood from the control cows developed anaplasmosis. It was concluded that long-acting oxytetracycline can be used to eliminate the naturally acquired carrier state of anaplasmosis in cattle.