| protection of cattle against heartwater in botswana: comparative efficacy of different methods against natural and blood-derived challenges. | five groups of tswana-cross castrated male cattle between 20 and 30 months of age (a total of 158 animals) were transported from a ranch in a heartwater-free area of south botswana to a feedlot near gaborone in the east of botswana where heartwater is endemic. on arrival, one group was vaccinated intravenously with the onderstepoort sheep blood heartwater vaccine, one group was vaccinated intravenously with the new onderstepoort tick-derived heartwater vaccine and a third group was vaccinated su ... | 1987 | 3604029 |