| Abstract: | Four-month-old Holstein-Friesian calves were inoculated with 3 different doses (1, 2, and 3 ml) of attenuated Anaplasma marginale vaccine. Vaccinated calves showed mild anaplasma parasitemia, slight decrease in packed cell volume, low serologic conversion, and no clinical illness. An artificial challenge exposure of vaccinated and unvaccinated calves with virulent Colombian A marginale showed that the vaccine provided protection against clinical signs of the disease, including parasitemia and anemia. The volume of the vaccinal dose did not alter the degree of protection provided. A 2nd group of 8- to 9-month-old Holstein-Friesian calves was then inoculated with 3 ml of anaplasma vaccine and premunized with both Babesia bigemina and Babesia argentina while being housed in an area free of these diseases. Calves were moved to an enzootic region heavily infested with various arthropods, including ticks, for natural field challenge exposure. Control calves, which were not given anaplasma vaccine, suffered clinical illness manifested by severe anemia and an average weight loss of 50.6 kg due to anaplasma field challenge exposure. In contrast, vaccinated calves did not show anemia and their weight loss was 3.9 kg. |
