Effects of concentrate supplementation on fecal microbiota, serum metabolomics, and proteomics in grazing Yili horses

Background Under grazing conditions, natural pasture alone may not fully meet the nutritional requirements of Yili horses. Seasonal variation and rainfall can also markedly affect pasture quality and nutrient composition, which may restrict the health management of Yili horses and the development of mare milk resources. Therefore, this study investigated the effects of concentrate supplementation on fecal fermentation parameters, serum metabolomic profiles, and serum proteomic profiles in grazing Yili horses. Materials and methods Sixteen healthy early-lactation Yili mares of similar age (3–4 years), foaling date (May 2023), and body weight (391.5 ± 13.74 kg) were randomly assigned to a grazing group (G) or a grazing plus concentrate supplementation group (GS), with eight mares in each group. Mares in the G group grazed naturally on pasture, whereas mares in the GS group received concentrate supplementation twice daily under grazing conditions, with 1 kg provided at each feeding (2 kg/day). The experiment lasted 100 days, including a 10-day adaptation period and a 90-day experimental period. On day 90 of the experimental period, fecal and blood samples were collected to determine fecal fermentation parameters, fecal microbial diversity, serum biochemical indices, serum metabolomic profiles, and serum proteomic profiles. Results Fecal fermentation and microbiota analyses showed that, compared with the G group, the GS group had significantly higher fecal propionate and butyrate concentrations, whereas fecal pH and the acetate-to-propionate ratio were significantly lower ( P  < 0.05). At the genus level, the relative abundances of Lachnoclostridium , Roseburia , Anaerosacchariphilus , and Coprococcus were significantly higher in the G group than in the GS group, whereas Treponema and Oliverpabstia were significantly less abundant in the G group than in the GS group ( P  < 0.05). Serum biochemical and metabolomic analyses showed that concentrate supplementation decreased total bilirubin (TBIL), total cholesterol (TC), and high-density lipoprotein cholesterol (HDL-C) concentrations, while increasing serum glucose (GLU) concentration ( P  < 0.05). Differential metabolites were mainly enriched in pathways related to the tricarboxylic acid cycle, nucleotide metabolism, bile secretion, vitamin B6 metabolism, and pyruvate metabolism. Serum proteomic analysis showed increased abundances of peroxiredoxin-5 (PRDX5), lactoylglutathione lyase (GLO1), transketolase, and several immune-related proteins, whereas phospholipid transfer protein, annexin, kallikrein-related peptidase 11, and several immunoglobulin light-chain fragments showed decreased abundance. Conclusions Concentrate supplementation under grazing conditions altered fecal fermentation patterns and fecal microbial composition in Yili horses, increased the production of fermentation products such as propionate and butyrate, and regulated pathways related to serum glucose and lipid metabolism, bile acid metabolism, antioxidant responses, and energy metabolism. These findings suggest that moderate concentrate supplementation may improve the nutritional and metabolic status of grazing Yili horses and provide a reference for feeding management during lactation.