Fermented mare’s milk, or koumiss, has been consumed for centuries across Central Asia for its nutritional and therapeutic value. Mare’s milk differs from bovine milk by its near 1:1 casein-to-whey ratio, high lysozyme and lactoferrin, abundant immunoglobulins, and low β-lactoglobulin, which enhance digestibility, reduce allergenicity, and increase antimicrobial activity. During fermentation, lactic acid bacteria and yeasts transform this substrate into a reservoir of bioactive proteins, peptides, and metabolites. Multi-omics profiling has identified more than 2300 peptides and over 350 metabolites, including sequences with angiotensin-converting enzyme (ACE)-inhibitory, antioxidant, antimicrobial, and immunomodulatory activities. Preclinical and limited clinical data indicate potential benefits for lipid metabolism, cardiovascular function, and gut health. Mechanistically, these effects appear to arise from synergistic actions of native proteins, fermentation-derived peptides, and probiotic consortia. Technological advances such as rational starter culture design, controlled proteolysis, and microencapsulation offer strategies to enhance bioactive yield and stability. However, standardized fermentation protocols and clinical validation remain necessary to position koumiss as a scientifically supported functional food.

Postnatal development in developing beef bulls is regulated through coordinated interactions among nutritional, metabolic, endocrine, and physiological processes that collectively determine structural maturation, reproductive competence, and breeding soundness. Optimizing these integrated regulatory mechanisms is essential for improving reproductive efficiency, accelerating genetic gain, and enhancing the sustainability of beef production systems. This review synthesizes current knowledge on the integrated regulation of postnatal development in developing beef bulls by combining evidence from developmental physiology, nutrition, metabolism, endocrine regulation, and reproductive biology. Particular emphasis is placed on tissue-specific maturation, nutrient-sensing and endocrine signaling, metabolic adaptation, developmental nutrient partitioning, pubertal development, and the biological mechanisms underlying breeding soundness. The review further evaluates practical approaches for assessing developmental progress using growth and structural traits, metabolic and endocrine biomarkers, reproductive indicators, and breeding soundness evaluation while highlighting the emerging roles of precision nutrition, precision phenotyping, multi-omics, wearable sensor technologies, artificial intelligence, and predictive modelling in developmental management. Current evidence indicates that postnatal development is governed by integrated biological networks rather than isolated physiological processes. Adoption of systems biology and data-driven approaches will facilitate earlier prediction of developmental competence, enable precision management of replacement sires, and improve reproductive efficiency, genetic progress, and the long-term sustainability of beef production.

Carcass weight (CW) is a major determinant of beef yield and market value in Korea, yet the genetic basis of this trait remains largely unexplored in cattle from Jeju Island. In this study, we performed a genome-wide association study (GWAS) using both a mixed linear model (MLM) and the FarmCPU approach, followed by pathway and network analyses to identify loci and biological functions underlying CW variation. A total of 256 Jeju cattle (92 Jeju Black and 164 Jeju Black × Hanwoo crossbreds) were initially sampled. One crossbred sample failed genotyping, leaving 255 animals (92 Jeju Black and 163 crossbreds) for analysis. Animals were genotyped using the Illumina BovineSNP50 v3 BeadChip, and 39,055 high-quality single nucleotide polymorphisms (SNPs) were retained after quality control. The MLM analysis detected no genome-wide significant associations, whereas the FarmCPU analysis identified six significant loci on Bos taurus chromosomes 3, 5, 6, 10, and 13, each explaining 2.55–9.58% of the phenotypic variance. Candidate genes located near these loci included EIF2B3, HECTD3, SOX5, KLF6, PHACTR3, and two uncharacterized protein-coding genes. Functional enrichment analysis identified biologically relevant pathways including lysine degradation, tryptophan metabolism, glycerolipid metabolism, fatty acid biosynthesis, extracellular matrix–receptor interaction, and signaling cascades such as PI3K–Akt and Rap1, although most pathways were not statistically significant after FDR correction. Protein–protein interaction (PPI) network analysis using STRING highlighted modules of signaling, extracellular matrix, and metabolic genes. These clusters suggest that coordinated interactions among these pathways contribute to carcass growth and development. These findings provide new insights into the molecular basis of CW in Jeju Black and Hanwoo × Jeju Black crossbred cattle and identify candidate genes and pathways that may be useful for genomic selection and the sustainable improvement of Jeju Black cattle populations.