Ecology of the cattle tick (Boophilus microplus) in subtropical Australia. II. Resistance of different breeds of cattle

Abstract

The resistance to the cattle tick, Boophilus mircoplus, of four herds of cattle with different Bos indicus (zebu) content, grazed at each of two locations in the subtropics of Queensland, Australia, was measured using artificial tick infestations at intervals of either 2 or 6 months over periods of up to 4 years. The factors affecting resistance of crossbred herds at each location in order of decreasing importance were the proportion of R. indicus genes, lactation, age interacting with nutritional conditions, a seasonal cycle which differed in timing at the two locations, and rainfall during the week of tick infestation. These variables accounted for 62% of the observed variation and the statistical model explained concurrent changes in resistance of other herds equally well. These findings are combined with data on the survival of freeliving stages of the ticks in a later paper to explain the observed variation in populations of cattle ticks on the untreated herds when grazing in separate pastures.