132. Identification of Candidate Genes Associated with Weaning Weight in Simmental Cattle.

Abstract Weaning weight is an economically important trait in beef cattle, as it reflects early growth, maternal ability, and calf development. In US Simmental cattle, the open-herdbook system may affect gene enrichment patterns by introducing alleles from other breeds that might alter the genetic architecture of this trait. This study aimed to explore the genetic structure of Simmental cattle by identifying candidate genes associated with weaning weight. A genome-wide association study (GWAS) was performed to identify genomic markers significantly associated with weaning weight. A linear mixed model was used, which included the fixed effects of contemporary group (defined as year-season-sex) and age at measurement in months, as well as expected heterosis of the animal, and maternal heterosis as linear covariates. The model also accounted for the random additive genetic effects, maternal effects, and residual. After applying Bonferroni correction (p < 0.05), gene annotation was performed for significant genomic regions using 100 kb flanking windows upstream and downstream of each significant SNP marker. In total, 13 SNPs were found to be significantly associated with weaning weight in this Simental population, which were located on chromosomes 5, 6, 10, 20 and 22. Within these regions, 26 candidate genes including protein-coding genes, long non-coding RNAs, ribosomal RNAs, and small nucleolar RNAs were identified. Six of these candidate genes (STC2, CREBRF, LAP3, TCF12, CAND2, and IFT122) are known to play important roles in growth and developmental processes. For instance, the STC2 gene influences body growth via the insulin-like growth factor signaling pathway, while the CREBRF gene is related to energy metabolism and body fat regulation. The LAP3 gene plays a role in protein metabolism and may enhance growth efficiency. Furthermore, genes associated with muscle differentiation and development were also identified, including TCF12, CAND2, and IFT122. The discovery of candidate genes driving metabolism, developmental signaling, and muscle growth underscores the complex polygenic architecture governing weaning weight in Simmental cattle. These findings not only elucidate the underlying biological mechanisms of early growth but also provide valuable genomic targets that could be integrated into breeding programs to optimize growth performance and production efficiency. Future research will focus on fine-mapping these regions to identify causal variants and evaluating their integration into genomic prediction models to accelerate genetic progress.