Prospection of differentially expressed genes related to the development of muscle fibers in Nellores calves submitted to different weaning protocols

Abstract

The Nellore breed was spread in Brazil into the half of the 20th century from India. At the begging of the decade 2000, the Nellore breed represented around 80% of the national beef cattle herd. The advantage of the zebu breed, as Nellore, is due to its ability to adapt to tropical weather. In the second half of the 20th century, successful national genetic improvement programs started to select animals with better productive and reproductive characteristics, such as weight gain and scrotal circumference, among others that are easy to measure. During the last years, together with the use of genomic tools and more accurate phenotype evaluation techniques, it has been seen the implementation of the improvement of characteristics related to the productive and early reproductive, as well as the quality of the carcasses and cuts. In addition, several nutritional management and protocols started to be tested and applied to Nellore cattle in different growth phases. These managements aim, directly or indirectly, to change characteristics related to meat quality. Between some of the management, the early weaning, that consists of calves weaning between 60 and 120 days old, which helped in improving the reproductive efficiency of the dam, also in Taurus breed, the research showing the change in early weaning calves' metabolism, as fat deposition and proportion of muscle fiber type. These changes occurred due to metabolic imprinting, which can alter muscle tissue development and lipid deposition during this phase. In this sense, the objective of this work will be to evaluate the differential expression of genes related to muscle fiber metabolism in Nellore calves submitted to different weaning protocols. For this, will be used 10 animals submitted at early weaning (120 days) and 10 animals submitted at conventional weaning (210 days). The animals from early weaning will be fed with concentrate in the feedlot and the calves from conventional will be kept with their dam in the pasture until 210 days. The RNA-seq method will be performed for sequencing the total messenger RNA from samples collected from calf's Longissimus thoracic using both groups at 210 days. Afterward, the sequences obtained (reads) will be aligned to the reference genome and, finally, the differentially expressed genes will be detected using the R program edgeR package. The results will be filtered according to the gene function and participation of metabolic pathways concerning the metabolism of skeletal muscle fibers. The results of this study will bring important information about adaptations in muscle metabolism of calves submitted to different postpartum diets. (AU)