Acquisition of resistance to the tick Amblyomma variegatum in Boran cattle, Bos indicus and the effects of Trypanosoma congolense and Babesia bigemina on host resistance.

Resistance was induced in cattle to the tick Amblyomma variegatum by five consecutive infestations with nymphs and adults. Using the principal component analysis (PCA), it was found that percentage of adults engorged, percentage of adults which died, percentage of nymphs which engorged, percentage of nymphs which moulted and percentage of nymphs which died, were the main indicators of resistance against A. variegatum. The percentages of nymphs which engorged or moulted after the third infestation were significantly (P < 0.01) reduced while the percentage of nymphs which died increased significantly (P < 0.01) after the third infestation. Percentages of adults which engorged or died started to decrease significantly (P < 0.01) from the fourth infestation after an initial increase during this period. The acquisition of resistance by cattle to the adult ticks was slower than to the nymphs. Infection of cattle with Trypanosoma congolense and Babesia bigemina after the fifth infestation enhanced the acquired immunity as revealed by the significantly (P < 0.01) increased feeding period of the adult ticks and changes in other parameters.