BREEDING FOR RESISTANCE TO BOOPHILUS MICROPLUS IN AUSTRALIAN ILLAWARRA SHORTHORN AND BRAHMAN X AUSTRALIAN ILLAWARRA SHORTHORN CATTLE

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Abstract
Breeding for resistance to the cattle tick B. microplus was undertaken in a herd of Australian Illawarra Shorthorn (AIS) cattle from 1961-1978 and in a herd of Braham .times. AIS cattle from 1970-1979. Breeder cows and their progeny were assessed for tick resistance during Oct.-Jan. Resistance levels were determined as the average percentage mortality of female ticks from 2 artificial infestations with cohorts of .apprx. 20,000 larvae. Resistance increased from 89.2% to 99% in the AIS breeding herd, as a result of the yearly introductions of more resistant individuals and culling of less resistant ones. Concurrently resistance in the AIS progeny increased from 93.7%-97.7%, demonstrating that the selection and breeding of the cows and bulls resulted in genetic improvement in the resistance of the progeny. Milk production tests on heifers from the selected AIS herd during 1975-1979 indicated that selection for tick resistance did not select against milk production. Resistance of the Brahman .times. AIS increased from 98.4-99.3% in the breeding herd and from 97.6% to 99.6% in the progeny. Female calves of both breeds were more resistant than males.

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