Identification of differentially expressed genes related to the development of muscle fibers during the early weaning period in Nellore calves

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 aim of our study will be to identify the gene expression related to muscle fiber metabolism of Nellore calves during two times of early weaning, before (120 days), and after (210 days). For this, we will evaluate skeletal muscle tissue biopsy (longissimus thoracis) at 120 days and 210 days old in the same group of 10 Nellore calves submitted at early weaning. These animals will be together of their dam in the pasture until the moment that will be weaning (120 days) and relocated to the paddock with concentrate supplementation until the final period (210 days). The RNA-seq will be used to analyze the total sequencing of messenger RNA. After, alignment of the sequences obtained (reads) will be carried out to the reference genome and, finally, the differentially expressed genes will be detected through the edgeR package of the R program and the results will be filtered according to the gene function and participation of metabolic pathways concerning the metabolism of the skeletal muscle fibers. Our results will bring important information about adaptations in muscle metabolism in calves submitted to different postpartum diets. (AU)