Field observations on adult zebu bulls immunised against anaplasmosis by infection and treatment plus integrated tick control.

Fourteen adult zebu bulls which were negative for Anaplasma marginale infection both serologically and on blood smear examinations were infected with a virulent Nigerian isolate of A. marginale. Forty days following the immunising infection when clinical reactions were established groups of seven animals were treated with either two doses of imidocarb dipropionate (2 X 5 mg/kg given intramuscularly 14 days apart) or a single intramuscular dose of long-acting oxytetracycline (5 mg/kg). Following clinical recovery, two weeks after the first treatment the immunised animals and seven susceptible controls were then introduced into a tick-infested area and held there for 15 months with regular tick control. There were significant differences between the mean weight gains of surviving animals in the oxytetracycline group and the controls and surviving animals in the imidocarb group and control cattle. The protective effect of tick control alone was inferior to that of integrated tick control plus anaplasmosis control by either method of immunisation. Losses occurred in all groups due mainly to the effects of other tick-borne diseases, babesiosis and heartwater.