Brazil has the largest commercial cattle herd in the world, with about 208 million head. The Brazilian herd consists mainly of Zebu and the Nelore breed has the highest expression as meat producer, with notable levels of economic performance. Feed efficiency is an important production trait of late and costly measurement, and despite its moderate heritability is not been included in the genetic evaluation programs in Brazil. Selection for more efficient animals may contribute to reductions in pasture area and pollutant production, despite a higher profitability for the producer. New methodologies for sequencing, genotyping and expression analysis technologies on a genome-scale have contributed to the knowledge of the genetic basis of variation and for the earlier selection in cattle. A previous project entitled "Genetic Strategies for quality beef production" produced 796 steers, offspring of 34 sires representing the diversity of Nelore. The steers were evaluated for feed efficiency and had their genotypes analyzed in the Illumina SNP BovineHD chip. This project identified genomic regions and genes associated feed efficiency. The present project aims to achieve a better understanding of the genetic mechanisms involved in variation in quantitative traits highlighted by the association analysis. Therefore, it is proposed to complement the analysis of genome wide association, expanding the functional analysis of the genome (RNA and microRNA), with the identification of microRNAs in muscle and liver tissue of Nelore cattle extremes for feed efficiency.
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