INHIBITION AND RECOVERY OF TICK FUNCTIONS IN CATTLE REPEATEDLY INFESTED WITH BOOPHILUS-MICROPLUS

Six tick-naive male Hereford calves were infested with about 18,000 Boophilus microplus larvae, 400 in a cloth bag, once a month for 6 mo. Working with the bag ticks, 12 tick characteristics were recorded for each infestation. Manifestations of resistance to some attributes appeared by the second infestation, peaked by the third (detachment weight, egg weight, fertility index) or fourth (feeding length, start of oviposition), and vanished by the fifth or sixth. Resistance to corpse weight, oviposition length, start of eclosion, feeding index, and survival developed more slowly but continued until the last infestation. Lymphocyte transformation after the fifth infestation was normal for concanavalin A and augmented in only 2 calves for phytohemagglutinin. In each infestation and at the end of all infestations some calves were significantly more resistant to some tick characteristics. There was no relationship between natural resistance and the ability to mount an acquired resistance. We concluded that B. microplus can depress or evade host's immunity, that resistance to different tick functions occurs independently, that natural and acquired resistance are unrelated, and that there exist genetic differences in natural or acquired resistance to the tick among seemingly homogeneous animals.