INTRODUCTION

Milk production is one of the most economically important traits in dairy goat production systems, particularly in high-yielding breeds such as Sapera goats. Sapera goats, developed through crossbreeding between Saanen and Etawah goats, are widely used as dairy goats in Indonesia because they combine relatively high milk production potential with adaptation to tropical production environments. Tropical environmental conditions may further influence lactation metabolism by affecting feed intake, energy balance, and physiological adaptation. Increasing global demand for dairy products has intensified the need to improve productivity and efficiency in dairy livestock while maintaining animal health and metabolic stability [1]. Milk yield is a complex trait influenced by multiple factors, including genetics, nutrition, physiological status, and metabolic regulation. Among these factors, metabolic adaptation plays a crucial role in determining lactating animals' ability to sustain high milk production. During lactation, animals experience substantial metabolic demands because large amounts of energy and nutrients are required to synthesize milk components such as lactose, milk fat, and milk proteins [2]. Therefore, understanding the metabolic mechanisms underlying variation in milk production is essential for improving dairy goat productivity and developing more effective management strategies.

Recent advances in metabolomics have provided powerful tools for investigating metabolic processes associated with animal productivity and physiological performance. Metabolomics enables comprehensive profiling of small-molecule metabolites that reflect an organism's biochemical state and provide insights into metabolic pathways that regulate physiological functions [3]. Because metabolites represent downstream products of gene expression and enzymatic activity, metabolomic analysis can capture functional changes in metabolic networks associated with physiological traits such as lactation performance [4]. In livestock research, metabolomics has increasingly been applied to identify metabolic biomarkers associated with milk production, metabolic efficiency, disease resistance, and nutritional status [5].

In dairy animals, lactation requires coordinated metabolic regulation of lipid, carbohydrate, and amino acid metabolism to meet the energetic and biosynthetic demands of milk synthesis. Lipid metabolism plays a critical role in providing energy substrates and structural components required for milk fat synthesis [6]. Carbohydrate metabolism, particularly glucose production through gluconeogenesis, is essential for lactose synthesis in the mammary gland, which ultimately determines milk volume [7]. Amino acid metabolism also contributes to milk protein synthesis and to metabolic signaling pathways that regulate nutrient utilization and cellular metabolism [8]. Consequently, alterations in these pathways may reflect physiological adaptations associated with different levels of milk production.

Despite the growing use of metabolomics in dairy animals, breed-specific information on serum metabolic signatures associated with differences in milk production remains limited in Sapera goats. Previous studies have mainly focused on dairy cattle or on general metabolic adaptations during lactation, whereas comprehensive characterization of serum metabolites associated with contrasting milk production phenotypes has received little attention in Sapera goats. Moreover, studies integrating biomarker discovery with metabolite enrichment and pathway topology analyses are scarce in this breed. Consequently, the biochemical mechanisms underlying variation in lactation efficiency and the metabolic pathways supporting superior milk production remain incompletely understood. Identification of such metabolic signatures could provide valuable insights into the mechanisms that regulate lactation and support the development of precision nutrition and management strategies to improve productivity and metabolic health in dairy goats [9].

We hypothesized that differences in milk production between high-production (HP) and low-production (LP) Sapera goats would be reflected by distinct serum metabolic signatures, particularly in pathways related to energy metabolism, lipid utilization, amino acid metabolism, and lactation-associated metabolic adaptation. Therefore, the present study aimed to investigate the serum metabolomic profiles of HP and LP Sapera goats using liquid chromatography-high resolution mass spectrometry (LC-HRMS). By integrating multivariate statistical analyses, biomarker identification, metabolite enrichment analysis, and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway topology analysis, this study sought to identify key metabolites and metabolic pathways associated with differences in milk production. The findings of this study are expected to provide new insights into the metabolic regulation of lactation and contribute to the development of metabolite-based biomarkers and nutritional strategies to enhance productivity in dairy goat production systems.