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Global gene expression and epigenetic changes in Nellore cattle submitted to different weaning protocols and their effect on carcass and meat quality


The Nelore breed has important hole in the national beef cattle production. Indian origin (zebuine), is extremely adapted to the tropical climate conditions dominant in the Brazil. However, in general, this breed was low productive, with lower residual intake feed, lower reproductive efficiency and lower meat quality, especially when compared to European beef cattle (taurine). Such difficult to measure and low heritability these traits have been improved with the biotechnology support, including the use of genomic data in the selection and differentially expressed gene analyzes. However, little has been done to understand epigenetic mechanisms in the regulation of gene expression within zebu breeds. As management techniques, early weaning, which consists of weaning calves between 60 and 90 days of age, has assisted in improving the reproductive efficiency of females, with sexual precocity in heifers, reduction of calving interval and increase of number of calves born per cow. In addition, in taurine beef cattle, this type of management has a great impact on the metabolism of calves weaned early, mainly by modifications of the epigenetic patterns, caused by the change of environment, of social and nutritional order. Such changes occur within an important nutritional window in the postpartum period leading to metabolic imprinting that can alter the way the muscle tissue develops and how the lipids settle into adulthood. Such management opens up the possibility of a nutritional contribution of good quality, rich in energy, which can lead to improvements in carcass and meat quality, and, if well conducted, to reduce the cycle for slaughter, especially when compared to those that remain under pasture under conventional weaning regime. Given the almost complete lack of information on epigenetic changes and gene expression in calves submitted to early weaning in the Nellore breed, as well as the relationship between these changes and meat quality, this study aims to analyze broadly the differences in expression and DNA methylation profiles in the weaning and adult stages, between nelores submitted to early weaning and conventional weaning. In addition, it aims to evaluate differences in carcass and physical-chemical aspects of the meat of animals submitted to different weaning protocols, as well as the relation of these characteristics with different levels of gene expression. To this end, 12 pre-weaned and 12 conventional weaned animals will be used, with biopsied tissue samples collected at three different points in time: early weaning (90 days old), conventional weaning (210 days of age) and immediately after slaughter (540 days of age). Such collections will be performed in both treatments and always in the same animals. Differences in gene expression and DNA methylation patterns between treatments will be analyzed through the sequencing of messenger RNA using the RNA-Seq and by the sequencing of genomic DNA using the RRBS (reduced regions bisulfite sequencing), respectively. Afterwards, the relationship between differentially expressed genes and adjacent differentially methylated regions will be evaluated; carcass differences and physic-chemical aspects of meat between treatments; and the possible relationship between differentially expressed genes and carcass and meat characteristics. (AU)

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