Estudo da infestação artificial de carrapatos (Boophilus Microplus) em fêmeas bovinas de diferentes grupos genéticos.

Abstract

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.