SILVA, Ana Mary da.; ALENCAR, Maurício Mello de.; REGITANO, Luciana Correia de Almeida.; OLIVEIRA, Márcia Cristina de Sena.
Resumo:
The resistance of beef cattle females to the cattle tick "Boophilus microplus" was evaluated by
artificial infestation of 66 animals of the following genetic groups: 16 Nellore (NE), 18 Canchim x Nellore
(CN), 16 Angus x Nellore (AN) and 16 Simmental x Nellore (SN). The animals, with mean age of 16.5
months, were maintained without chemical tick control in a "Brachiaria decumbens" pasture. Four artificial
infestations with 10,000 larvae, 14 days apart each, were done, and from day 19 to day 23 of each infestation the number of engorged females ticks was counted on the left side of the animal. The data were
analyzed as the percentage of return (PR = percentage of ticks counted relative to the number infested,
transformed to PR"1/4"), using the least squares method with a model that included the effects of genetic
group (GG), animal within GG (error a), infestation number (I), GG x I, and the residual (error b). The
results indicated a significant GG x I interaction, with the AN and SN showing higher percentage return
than the CN and NE animals, while the CN animals showed higher percentage return than the NE ones
only in infestations 3 and 4. The transformed percentage return were 0.399, 0.649, 1.056 and 1.013, for the
NE, CN, AN and SN, respectively.