Determinação da resistência ou susceptibilidade de bovinos ao carrapato Rhipicephalus microplus avaliado à campo através de infestação artificial

Abstract

The control of the tick Rhipicephalus microplus represents a challenge for Brazilian cattle farming and, as a result, is the subject of numerous studies. This ectoparasite can transmit pathogens responsible for Cattle Tick Fever (CTF) and directly impact milk and meat production, as well as promote the occurrence of myiasis in animals. Acaricides are the methods used to control this tick with proven effectiveness. However, their uncontrolled use has contributed to the development of resistance in tick populations against the products employed. Due to this problem, tick control methods need to be constantly evaluated. In these assessments, it is crucial to determine whether the reduction in the number of ticks in the parasitic phase is due to the effectiveness of a product or the immune resistance of the host. However, in field studies, there is another factor that must be considered: the movement of animals in an infested pasture and their uneven exposure to infestations. This movement can expose animals irregularly to the infestations, complicating the interpretation of the level of resistance of the cattle to the tick. This study aimed to evaluate a new methodology for analyzing cattle resistance and immune susceptibility to ticks, through artificial infestations and weekly counts of engorged females, and compare these results with those from natural infestations. Characterizing the degree of resistance allows for a homogeneous division of experimental groups for subsequent control method testing and determines whether it is associated with the animals' breed. The artificial infestations allowed for the discernment of cattle resistance levels to ticks and support previous studies showing that European-origin cattle are more susceptible to ticks than those of Indian origin. Our results also validate the assessment of cattle resistance to ticks following a natural infestation, as the results were like those obtained from artificial infestations with a predetermined number of larvae.