The effect of season and nutrition on the resistance of cattle to the tick Boophilus microplus

Abstract

The host resistance of Bos tauvus (British) and B. indicus x B. tauvus (Zebu x British) steers and heifers to cattle tick (Boophilus microplus) was measured at about monthly intervals for periods of up to 2: years in south-eastern Queensland. The cattle either grazed native pasture, with or without a supplement of lucerne pellets, or were fed entirely on lucerne pellets in yards. Animals grazing native pastures, with poor quality feed in late-autumn and winter, suffered substantial losses of resistance. Up to five times as many ticks survived on them in autumn-winter as in spring-summer, regardless of breed. A less-marked cycle of resistance was observed on all animals fed on lucerne or lucerne supplement, with 2-3 times as many ticks reaching maturity from a constant infestation of larvae in autumn-winter as in spring-summer. Zebu x British steers yielded the same numbers of ticks as heifers in winter but twice as many as heifers in summer. No difference was observed in the yield of ticks from the heifers and steers of British breed at any time. A hypothesis is proposed that the primary cause of the seasonal loss of resistance is the hosts' physiological response to shortening photoperiod. Recovery of resistance is spontaneous once some adaptation to winter conditions has been completed, usually around the time of the winter solstice. Nutritional stress accentuates the loss of resistance and delays its recovery.