Resistance to the tick Boophilus microplus on cattle in Colombia: skin testing to select resistant cattle under tropical conditions

Abstract

The feasibility of using, in Colombia, skin testing for selecting cattle of good ability to acquire resistance to the tick Boophilus microplus was investigated. The skin test used tick antigens isolated by chromatographic fractionation of whole ticks or dissection and homogenisation of salivary glands. Antigens were injected intradermally and the size of the macroscopic reactions was measured. The protein composition and antigenicity of different batches of antigens were compared by electrophoresis with polyacrylamide gels and by Western blotting. The enzyme-linked immunosorbent assay was used to relate anti-tick antibodies to individual resistance to ticks. A preliminary investigation used rabbits infested with Rhipicephalus appendiculatus ticks, then different groups of cattle in four separate experiments were infested with B. microplus and individual resistance to ticks assessed by counts of ticks.

Skin test reactions in rabbits were mainly of the delayed hypersensitivity type. Their correlation with individual resistance was positive and significant. Skin test reactions in cattle were immune specific and mainly of the immediate hypersensitivity type. Their correlation with individual resistance was highly variable between individuals and experimental groups and showed to be affected by environmental factors. The reproducibility of isolation of batches of antigens from ticks was good. Antibody titres correlated positively with low resistance to ticks, but high antibody levels interfered with the skin test reactions. It was concluded that this skin test could be used with the serological test for the practical selection of animals that have already acquired resistance by natural infestation. The test could also be used to measure the adaptability of individuals to environmental stress.