PS2-2. Characterization of Differentially Expressed Genes in Abscessed and Non-abscessed Livers of Beef x Holstein Feedlot Steers

Liver abscesses (LA) cause economic losses due to carcass trimming and liver condemnations. Additional feedlot performance losses associated with LA may be caused by impaired liver function and metabolism. This study aimed to identify differentially expressed genes (DEG) in abscessed livers (AL) and non-abscessed livers (NL). Beef × Holstein steers (n = 60) were fed finishing diets containing 20 or 40% corn silage (20CS or 40CS) on a DM basis. Steers were allocated to five pens per diet and harvested after reaching 31% empty body fat, predicted by ultrasound, after 286 (20CS) and 293 (40CS) d on feed. Six representative AL were selected from steers fed 20CS (LA incidence = 40%) and six representative NL were selected from steers fed 40CS (LA incidence = 3%). Liver samples were collected at harvest from the left lobe, a minimum of 15 cm from any abscess. Total RNA from samples were sequenced in 2x150 bp format on an AVITI instrument. Reads were mapped to the Bos taurus reference genome (ARS-UCD2.0), and gene counts were obtained using HTSeq. Differential expression between AL and NL was analyzed using DESeq2. The DEGs were defined as genes with an adjusted-P < 0.10 and underwent gene set enrichment analysis via the g:GOSt function of g:Profiler. A total of 92 DEGs were identified, with 51 upregulated and 41 downregulated in NL compared with AL. Selection of DEGs of interest (5 upregulated, 5 downregulated) was based on their direct relationship to liver function and metabolism. Although DEGs of interest were not correlated with average daily gain, there were correlations with dry matter intake (DMI) and gain to feed (G:F). Genes associated with metabolic and energetic functions, such as MPC1, APOA4, GK5, CPOX, and ADIPOR2 were upregulated in NL. These upregulated genes were positively correlated with dry matter intake (DMI; R > 0.60, FDR < 0.10) and negatively correlated with G:F (R > -0.45, FDR < 0.22). These findings suggest that upregulation of genes associated with metabolic function may increase energy demand. Upregulated genes, specifically MPC1 and GK5, have been associated with less efficient nutrient utilization, consistent with a negative correlation with G:F. Genes associated with liver stress, inflammation, and tissue remodeling, such as TNC, IRF6, HPX,CMKLR2, and ERBB2, were downregulated in NL. Downregulated genes were negatively correlated with DMI (R > -0.50, FDR < 0.33), but positively correlated with G:F (R > 0.38, FDR < 0.78). Downregulated genes such as IRF6 and CMKLR2 are associated with enhanced feed efficiency. This suggests that the downregulated genes may be associated with healthier liver function and reduced immune activation. Overall, these data support that LA may have negative impacts on feedlot performance by altering liver health and metabolism.