PSXIII-28 Hepatic transcriptome analysis of beef steers with divergent Residual body weight gain.

Abstract This study utilized hepatic transcriptome profiling to investigate key genes and metabolic pathways associated with divergent Residual Average Daily Gain (RADG) phenotypes in crossbred beef steers. A total of 108 steers (average BW = 556 ± 38 kg) were fed a high-forage total mixed ration for 49 days in five dry lot pens equipped with GrowSafe8000 intake nodes to determine RADG. After ranking the steers by RADG coefficients, liver biopsies were collected from the most efficient (n = 8; 0.73 kg/d) and least efficient (n = 8; -0.69 kg/d) steers under local anesthesia. Approximately 1g of liver tissue was collected and preserved in RNA later solution for transcriptomic analysis. Total RNA was extracted and used for library construction, followed by mRNA purification, cDNA synthesis, end repair, adapter ligation, and sequencing on an Illumina NovaSeq 6000 platform. Raw sequence data were processed to remove low-quality reads (Qscore ≤ 5) and aligned to the Bos taurus ARS-RCD1.3 reference genome using STAR aligner. Differential gene expression analysis was performed using DESeq2, identifying 514 differentially expressed genes (DEGs) with a significance threshold of p ≤ 0.05 and log2(FC) > log2(1.2). Among these, 171 genes including IGF1, CXCL8, ARG2, and SLC2A5 were upregulated in positive RADG steers, while 343 genes including CASP16, CNR1, and GNRA4 were downregulated. GO Enrichment Analysis (GEA) revealed that enriched pathways in positive RADG steers included the regulation of extrinsic apoptotic signaling, DNA-dependent DNA replication, and cellular components such as collagen-containing extracellular matrix, acrosomal vesicles, and sarcolemma. Additionally, molecular functions related to carbohydrate transmembrane transport, monosaccharide binding, and antioxidant activity were enhanced. Conversely, pathways such as negative regulation of ossification, guanyl ribonucleotide binding, multicellular organismal response to stress, and killing of cells of other organisms were downregulated. These changes suggest that positive RADG steers exhibit improved feed efficiency, growth, and resilience. Enhanced apoptotic regulation and DNA replication may facilitate efficient cell turnover and muscle development, while improved extracellular matrix and sarcolemma function support muscle integrity. Increased carbohydrate transport and antioxidant activity may enhance energy utilization and stress resistance. The downregulation of ossification regulation may promote balanced skeletal and muscle growth, optimizing structural development. Reduced guanyl ribonucleotide binding activity could improve metabolic efficiency by refining cellular signaling. A decreased stress response suggests lower physiological strain, potentially enhancing feed conversion. Moreover, a moderated immune response may prevent unnecessary energy expenditure, further supporting growth efficiency. This study highlights key genetic and metabolic adaptations influencing RADG phenotypes in crossbred beef steers.