Exploring the Genetic Basis of Residual Feed Intake (RFI) for Predicting Feed Efficiency in Beef Bulls

Residual feed intake (RFI) is defined as the difference between actual feed consumption and the predicted feed intake based ona bull’s live weight, growth, and maintenance needs. Bulls with low RFI values are considered more efficient because they havereduced feed costs compared to those with high RFI values. Identifying marker genes that control RFI is challenging due to thesignificant variation in differentially expressed genes (DEGs) and the antagonistic expression of genes that regulate the RFI traitin bulls. In this literature review, we searched for potential genes, their positional single nucleotide polymorphisms (SNPs), theirchromosomal locations, and their expression patterns to better understand the regulation of RFI traits in bulls. Based on spe-cific inclusion criteria, this review explored over 200 studies on RFI in beef bulls and steers published between 2012 and 2022.The review utilized genome-wide association studies (GWAS) and gene set enrichment analysis (GSEA) and identified 511 geneslocated on 240 chromosomal loci in 7,992 beef bulls. Of these genes, 52 were consistently reported as modulating RFI, while 469were unique and only reported once. During this period, 228 of the 244 chromosomal loci were reported multiple times, while16 were reported only once. The literature search revealed that 11 studies linked the bovine chromosome 6 (BTA6) to RFI quan-titative trait loci (QTLs) in bulls. Similarly, eight studies linked BTA8, ten linked BTA7, and eight linked BTA11 to RFI QTLs. Ad-ditionally, 228 SNPs were identified across 30 chromosomal locations between 2012 and 2023. This review provides novel in-sights into the molecular mechanisms underlying feed efficiency (FE) regulation and lays the groundwork for identifying mo-lecular markers associated with FE in bulls across all breeds and populations.