Parâmetros genéticos para resistência aos carrapatos, helmintos gastrointestinais e Eimeria spp. e perspectivas do uso de seleção em bovinos da raça Nelore

Abstract

Parasitism caused by Rhipicephalus (Boophilus) microplus, gastrointestinal nematodes and Eimeria spp. is responsible for productive and economic losses in the beef business. Traditional methods for parasite control allow the use of chemical antiparasite products that can lead to parasite resistance against those products. Such substances also could leave residues in meat. It is important to know the different resistance mechanisms against ticks, gastrointestinal nematodes and Eimeria spp. in cattle to develop alternative ways for parasite control such as selection of resistant animals. The objective of this study was to quantify the genetic variability of Nellore cattle against ticks (TICK), gastrointestinal nematodes (EPG) and Eimeria spp. (EIM) at 205 and 550 days of age. Posterior means (high density interval with 95% of samples) of heritability were 0.16 (0.01; 0.40), 0.28 (0.03; 0.60) and 0.24 (0.01; 0.50) for resistance to ticks, gastrointestinal nematodes and Eimeria spp. at 205 days of age, respectively. At 550 days of age, these values were 0.11 (0.00002; 0.31), 0.11 (0.001; 0.37) and 0.57 (0.05; 0.9) respectively. Posterior means (high density interval with 95% of samples) of genetic correlations among TICK205 x TICK550, EPG205 x EPG550 and EIM205 x EIM550 were -0.17 (-1.00; 0.98), -0.37 (-0.97; 0.48) and 0.16 (-0.70; 0.89), among TICK205 x EPG205, TICK205 x EIM205 and EPG205 x EIM205 were -0.14 (-0.99; 0.70), -0.60 (-1.0; 0.84) and 0.16 (-0.78; 0.99), among TICK550 x EPG550, TICK550 x EIM550 and EPG550 x EIM550 were -0.37 (-0.96;0.50), 0.74 (0.11;1.0) and -0.04 (-1.0;0.93) respectively. There is genetic variability for parasite resistance and selection could contribute for increasing the frequency of resistant animals in Nellore breed. The genetic correlations are associated with wide high density intervals that included zero in the majority of situations, and selection for increasing resistance must be done for each trait and in both ages.