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 Bo ophilus microplus larvae, 400 in a cloth bag, once a month for 6 mo. W orking with the bag ticks, 12 tick characteristics were recorded for e ach infestation. Manifestations of resistance to some attributes appea red by the second infestation, peaked by the third (detachment weight, egg weight, fertility index) or fourth (feeding length, start of ovip osition), and vanished by the fifth or sixth. Resistance to corpse wei ght, oviposition length, start of eclosion, feeding index, and surviva l developed more slowly but continued until the last infestation. Lymp hocyte transformation after the fifth infestation was normal for conca navalin A and augmented in only 2 calves for phytohemagglutinin. In ea ch infestation and at the end of all infestations some calves were sig nificantly more resistant to some tick characteristics. There was no r elationship between natural resistance and the ability to mount an acq uired resistance. We concluded that B. microplus can depress or evade host's immunity, that resistance to different tick functions occurs in dependently, that natural and acquired resistance are unrelated, and t hat there exist genetic differences in natural or acquired resistance to the tick among seemingly homogeneous animals.