Estudo genético de características de resposta a parasitoses em bovinos criados em regiões tropicais

Abstract

Parasites cause significant loss at livestock industry and for different species of interest. At tropical regions, specially, parasitosis are endemic and their impact on livestock are even more expressive. This phenomenon happens because in these tropical regions edaphoclimatic conditions favour both the proliferation and the dissemination of parasites in the infecting stage. The material presented here has the objective of demonstrate the importance of the main parasites that affect the beef cattle production system and genetic characterize both the resistance and the resilience to parasites, presenting the different biological mechanisms by which animals respond to the parasite burden. We will present here two studies: the first is a study focused on the differences observed at host resistance to ticks in two populations, one of Nellore cattle raised in Brazil and the other of Tropical Composite cattle raised in Australia; the second aims to genetic characterize host resilience to ticks, gastrointestinal nematodes, and coccidia at a Nellore population across ages. In this thesis we demonstrated that there is genetic variability for both studied traits: resistance and resilience, even for the Nellore population, in which the observed parasite burdens were low. Also, our preliminary results demonstrate that the biological mechanisms associated with resistance to ticks at both Nellore and Tropical Composite populations are partially distinct, and that possibly the racial composition (Bos taurus x Bos indicus) interferes in the expression of the studied mechanism of response to parasitosis. Regarding host resilience to different parasites, we verified that mechanisms associated to its expression differ according to both animal’s age (which is probably associated with immune system maturation), and regarding the studied parasite. The results presented in this thesis open space to the discussion of immune mechanisms evolved in the different phenotypes, of the differences observed in the response to disease across ages or between breeds (mainly regarding differences that are expected in host resistance between zebu and indicine animals).