Comparative analysis of Rhipicephalus microplus (Canestrini, 1888) infestation in pure breed (Hereford) and cross breed (Braford) cattle herds subjected to the same chemical treatments

Abstract

The aim of this work was to analyze the R. microplus (Canestrini, 1888) infestation in twobovine herds with different degrees of natural resistance (i.e., Hereford and Braford) toticks subjected to an identical chemical treatment scheme to ticks at the same farm, to demonstratethe impact on tick control of the incorporation of a more resistant bovine breed.Two groups of ten Hereford and Braford cows each were subjected to eleven chemicaltreatments between August 2022 and October 2023 (four fluazuron, two fipronil 1%, oneivermectin 3.15% and four immersion in a dipping vat with a combination of cypermethrin10% and ethion 40%). Tick population was shown to be susceptible to ivermectin,fluazuron and the mix cypermethrin 10%-ethion 40% and resistant to fipronil accordingto in vitro tests. Tick infestation was significantly greater in the Hereford cows than in theBraford cows. Tick infestation in both Hereford and Braford breeds was similar when treatmentwith functional drugs was applied, but when a block of the treatments was done withdrugs with decreased functionality due to resistance (i.e. fipronil), treatment failure wasmanifested more strongly in the most susceptible breed. The incorporation of cattle breedswith moderate or high resistance to R. microplus is instrumental to optimize the efficacyand sustainability of chemical control of ticks in a scenario where resistance to one ormore chemical groups is almost ubiquitous, because it favors the biological control of thisparasite.