Muscle fibers, as the fundamental units of muscle tissue, play a crucial role in determining skeletal muscle function through their growth, development, and composition. To investigate changes in muscle fiber types and their regulatory mechanisms in Mongolian horses (MG), Xilingol horses (XL), and Grassland-Thoroughbreds (CY), we conducted histological and bioinformatic analyses on the gluteus medius muscle of these three horse breeds. Immunofluorescence analysis revealed that Grassland-Thoroughbreds had the highest proportion of fast-twitch muscle fibers at 78.63%, while Mongolian horses had the lowest proportion at 57.54%. Whole-transcriptome analysis identified 105 differentially expressed genes (DEGs) in the CY vs. MG comparison and 104 DEGs in the CY vs. XL comparison. Time-series expression profiling grouped the DEGs into eight gene sets, with three sets showing significantly up-regulated or down-regulated expression patterns (p < 0.05). Additionally, 280 differentially expressed long non-coding RNAs (DELs) were identified in CY vs. MG, and 213 DELs were identified in CY vs. XL. A total of 32 differentially expressed microRNAs (DEMIRs) were identified in CY vs. MG, while 44 DEMIRs were found in CY vs. XL. Functional enrichment analysis indicated that the DEGs were significantly enriched in essential biological processes, such as actin filament organization, muscle contraction, and protein phosphorylation. KEGG pathway analysis showed their involvement in key signaling pathways, including the mTOR signaling pathway, FoxO signaling pathway, and HIF-1 signaling pathway. Furthermore, functional variation-based analyses revealed associations between non-coding RNAs and mRNAs, with some non-coding RNAs targeting genes potentially related to muscle function regulation. These findings provide valuable insights into the molecular basis for the environmental adaptability, athletic performance, and muscle characteristics in horses, offering new perspectives for the breeding of Grassland-Thoroughbreds.

Speed and endurance are the primary goals in racehorse breeding. The Grassland-Thoroughbred is a newly developed breed in northern China that combines speed, endurance, and environmental adaptability. However, current research on the genetic background of this breed and the genes associated with athletic performance remains limited. We conducted whole-genome resequencing on Mongolian (MG), Thoroughbred (TB), Xilingol (XL), and Grassland-Thoroughbred (CY) horses, generating 3813.74 Gb of clean data after quality control. The number of transitions was significantly higher than that of transversions. The SNPs were mainly located in intergenic regions, followed by intronic regions. Principal component analysis, population structure analysis, and phylogenetic tree results indicated that the CYs had a distinct genetic background from MGs, TBs, and XLs, but based on PCA and phylogenetic clustering, they showed greater genetic similarity to Thoroughbreds. Using fixation index (Fst) and nucleotide diversity ratio (π ratio) analyses between CYs and the other three horse populations, 70, 76, and 80 candidate genes were identified from the intersection of the two methods, respectively. A total of 179 candidate genes were obtained from the union of the three groups. Candidate genes associated with athletic performance (ATF2, NDUFS7, PRKG1, IGFN1, MTOR, TTN) and growth and development (MTOR, IGFN1, COL21A1, NEDD4, PIEZO1) were screened. These genes are related to athletic ability and developmental processes in the CY population. Our study reveals genomic information associated with important traits in Grassland-Thoroughbreds and identifies valuable candidate genes, laying a foundation for future breeding and trait association studies.

The core objective of racehorse breeding is to enhance the speed and endurance of the horses. The Grassland-Thoroughbred is an emerging horse breed developed in northern China in recent years, characterized by excellent speed performance, enduring stamina, and strong environmental adaptability. However, research on the genetic characteristics within this breed and the genes associated with athletic performance remains relatively limited. We conducted whole-genome resequencing of Grassland-Thoroughbred F1, F2, F3, and the crossbred population (CY) and obtained a total of 4056.23 Gb of high-quality data after quality control. The single nucleotide polymorphisms (SNPs) were primarily distributed in intergenic regions, followed by intronic regions. Principal component analysis (PCA) and STRUCTURE revealed clear distinctions among the generations, with a notable overlap between CY and F3. Using the SNP dataset, we analyzed the number and length distribution patterns of runs of homozygosity (ROHs) in the genomes of different generational groups of Grassland-Thoroughbreds. Short ROHs ranging from 0.5 to 2 Mb were the most abundant, with the following distribution: F1 (85.15%) > F2 (82.92%) > CY (78.75%) > F3 (77.51%). Medium-length ROHs (2–8 Mb) and long ROHs (>8 Mb) together exhibited a similar but opposite trend. The average length of ROHs was 1.57 Mb. The inbreeding coefficients (F_ROH) among different generational groups of Grassland-Thoroughbreds were as follows: F1 (0.0942) < F2 (0.1197) < CY (0.1435) < F3 (0.1497). Through ROH island analysis, 10 high-frequency ROH regions were identified and annotated with 120 genes. Genomic regions and candidate genes associated with athletic traits—ACAD8, OPCML, PRDX2, NTM, NDUFB7, SCL25A15, FOXO1, and SLC4A10—were identified. These genes may play important roles in regulating muscle performance, mitochondrial energy supply, and learning and memory processes in horses and are closely associated with the athletic ability of the Grassland-Thoroughbred population. This study is the first to systematically characterize the genomic diversity and inbreeding dynamics of the Grassland-Thoroughbred during the breeding process. It identifies candidate genes that may influence athletic performance, thereby providing an important molecular foundation and theoretical basis for the genetic improvement and performance-based selection of this emerging breed.

Speed is not only the primary objective of racehorse breeding but also a crucial indicator for evaluating racehorse performance. This study investigates a newly developed racehorse breed in China. Through whole-genome resequencing, we selected 60 offspring obtained from the crossbreeding of Thoroughbred horses and Xilingol horses for this study. This breed is tentatively named “Grassland-Thoroughbred”, and the samples were divided into two groups based on racing ability: 30 racehorses and 30 non-racehorses. Based on whole-genome sequencing data, the study achieved an average sequencing depth of 25.63×. The analysis revealed strong selection pressure on chromosomes (Chr) 1 and 3. Selection signals were detected using methods such as the nucleotide diversity ratio (π ratio), integrated haplotype score (iHS), fixation index (Fst), and cross-population extended haplotype homozygosity (XP-EHH). Regions ranked in the top 5% by at least three methods were designated as candidate regions. This approach detected 215 candidate genes. Additionally, the Fst method was employed to detect Indels, and the top 1% regions detected were considered candidate regions, covering 661 candidate genes. Functional enrichment analysis of the candidate genes suggests that pathways related to immune regulation, neural signal transmission, muscle contraction, and energy metabolism may significantly influence differences in performance. Among these identified genes, PPARGC1A, FOXO1, SGCD, FOXP2, PRKG1, SLC25A15, CKMT2, and TRAP1 play crucial roles in muscle function, metabolism, sensory perception, and neurobiology, indicating their key significance in shaping racehorse phenotypes. This study not only enhances understanding of the molecular mechanisms underlying racehorse speed but also provides essential theoretical and practical references for the molecular breeding of Grassland-Thoroughbreds.

Copy number variation (CNV) is an important source of genetic variation. However, studies utilizing whole-genome sequencing to investigate CNVs in horse populations and their effects on traits remain relatively limited. This study aims to address the lack of research on the impact of copy number variation (CNV) on racing performance in horse populations, providing new insights for locally bred racing breeds. We analyzed 60 offspring derived from the crossbreeding of Thoroughbred horses and Xilingol horses. These horses were temporarily named “Grassland-Thoroughbred” and were divided into two groups: 30 racing horses and 30 non-racing horses. A total of 89,527 CNVs were identified. After merging overlapping CNVs, 982 copy number variation regions (CNVRs) were recognized, among which the racing horse group (RH) had 29 unique CNVRs, while the non-racing horse group (NR) had 4 unique CNVRs. In addition, a total of 195 genes overlapping with CNVRs were identified. Transcriptomic analysis revealed 120 differentially expressed genes, with MTPN expressed in both CNVR-overlapping genes and mRNA. Both CNVR-overlapping genes and differentially expressed genes were enriched in the MAPK signaling pathway; CNV may affect gene expression through gene dosage effects or regulatory mechanisms. Using Vst statistical analysis, we further screened candidate CNVRs in autosomes that exceeded the 95% differentiation threshold between the RH and NR populations. Several key genes associated with energy metabolism and muscle function were identified, including AGT, IGFN1, IMMPL2, SLC41A3, AOX4, and ACAD11. These findings provide new insights into the genetic structural variation in racing performance and adaptability, fill the gap in CNV studies in the genomics of Grassland-Thoroughbred horses, and offer valuable genomic data for optimizing breeding strategies in native racing horse populations.

Ferulic acid is a bioactive phenolic compound with potential benefits for skeletal muscle health. In this study, Mongolian horses were used as experimental subjects and were orally administered ferulic acid at doses of 5, 10, or 15 g per horse per day for 40 consecutive days. Muscle biopsy samples were analyzed using proteomics to assess fiber type composition and regulatory protein expression. Ferulic acid supplementation increased the proportion of fast-twitch fibers and upregulated key differentiation factors such as MUSTN1, while modulating glycolysis, ECM remodeling, and calcium signaling pathways. Although ferulic acid induced moderate oxidative stress, it did not trigger classical ferroptosis. Collectively, these findings demonstrate that ferulic acid promotes fast-twitch fiber transformation in horses through coordinated metabolic and signaling mechanisms, highlighting its potential as a nutritional strategy to enhance skeletal muscle adaptability and athletic performance in horses.