Resistance by cattle to cattle tick, Boophilus microplus. III. The development of resistance to experimental infestations by purebred Sahiwal and Australian Illawarra Shorthorn cattle
Purebred Sahiwal cattle acquired resistance to Boophilus microplus in a similar manner to crossbred Sahiwal cattle as previously reported. The purebred entire males and females were more resistant than a control group of crossbred steers because they dropped significantly fewer replete ticks than the crossbreds at the third and fourth, but not at the first and second infestations. Adult female ticks dropped by purebred animals were significantly lighter than those dropped by crossbred animals at the fourth infestation only. There was no significant difference in the numbers of eggs laid and hatched from ticks dropped by purebred and crossbred animals. Australian Illawarra Shorthorn steers developed resistance at a second and third infestation which waned at a fourth infestation, but individual steers displayed developing resistance throughout the four infestations. Day of modal drop of replete female ticks appeared to be affected by breed, and developing resistance or season.