Delineamento de esquemas de seleção genômica para resistência ao carrapato bovino

Abstract

The objective of this study were compare the gains from the inclusion of genomic values in the selection index (IS) and check the cost benefit of the incorporation of genomic selection in Delta G Hereford and Braford breeding program, adding the trait count of ticks (CARR) using IS. Besides CARR, traits already considered in Delta G Index (IDG) were evaluated: pre-weaning gain (GPND), weaning conformation (CD), weaning precocity (PD), weaning muscling (MD), post-weaning gain (GPPD), yearling conformation (CS), yearling precocity (PS), yearling muscling (MS) and scrotal circumference (PE). Genetic gain per generation (ΔG) was evaluated using nine different SI, the current IDG and eight alternatives that included RES in the IDG with 10%, 50% or 100% relative weight, using traditional (EBV) or genomic (GEBV) breeding values. For selection with selective genotyping, seven strategies were considered with relative weight in CARR 0%, 50% or 100% using EBV or GEBV, selecting and genotyping all or part of animals weaning and yearling. Accuracy of GEBV (rMG) ranged from 0.1 to 0.9. Changes in the accuracy of the IS ( IH R )changing rMG were higher for scenarios involving GEBV with all the traits in the index (0.16 to 0.96), compared to scenarios where only CARR was considered to GEBV (0.37 to 0.82). Counting ticks and using EBV to select for RES would result in the same ΔG of a GEBV with rMG=0.44, but animal would have to be exposed to parasite to obtain the phenotypic information. On the other hand, use of GEBV for RES with rMG ≥ 0.5 would result in higher values for IH R ranging from 0.50 to 0.93, without the risks of parasitism. Total gains increased and the differences from baseline were expanded when the relative weight by CARR was 50%. Higher differences were observed between the control scenario and the scenario using EBV with 100% weight for CARR, when compared to the control and the scenarios with 10 and 50% containing only EBV. Due to the low correlation with other traits of IDG, the substantial genetic progress for CARR would only be achieved when the main focus of selection, 50% CARR GEBV (ΔG = 37.40) or all traits with GEBV (ΔG = 42.00 ). The selection without genotyping of the animals, the return on genetic gain (RG) is greater (RG = 0.004) with lower cost (R $ 221.00 reais) genotyping that all animals (RG = 0.001 and cost R$ 694, 00 reais) to increase a genetic standard deviation. In the study, for selection focused on CARR indexes with GEBV information with 50% weight outperform emphasizing the trait, when the goal is to get animals resistant to parasitism. The selective genotyping, the strategy with greater genetic gain and lower cost to increase a DP and mair return in genetic gain is using 100% weight for genotyping CARR 25% of male yearling.