Relationship between the resistance of cattle to Haemaphysalis longicornis and to Boophilus microplus.

Cattle that had been exposed to Haemaphysalis longicornis were as susceptible to Boophilus microplus as cattle that had never been exposed to either species of tick. Cattle with acquired resistance to both species ranked consistently for levels of resistance to each when infested separately. Concurrent infestation with H. longicornis had no effect on ranking for resistance to B. microplus. The coefficient of concordance between the rankings of individuals on their levels of resistance to both species of tick was positive, but was not statistically significant. We conclude that the tick antigens that stimulate host resistance are species-specific and do not cross protect. The apparent correlation in rankings for resistance to the 2 species may be a consequence of either an individual's immunological responsiveness to tick antigens or to non-specific host factors which determine levels of resistance. The apparent correlation suggests that co-selection for resistance to different tick species is practicable.