This study investigated the effects of dietary mannan oligosaccharide (MOS) supplementation on growth performance, serum biochemistry, metabolomic profiles, and fecal microbiota in lactating Dezhou donkeys. Sixteen healthy jennies and their foals were randomly allocated to a control group (MCON), a group receiving no MOS, or an MOS-supplemented group (MMO; 0.5 g/kg diet) for 60 days. Compared with the MCON group, the MMO group showed a mitigation of lactational weight reduction, improved serum protein profiles, and favorable modulation of lipid metabolism. Furthermore, serum metabolomic analysis revealed 102 differentially abundant metabolites, which were enriched in 17 KEGG pathways involved in energy metabolism, bile secretion, and anti-inflammatory signaling. Key metabolites such as L-4-Chlorotryptophan, Gly-Trp, and cholylthreonine indicated enhanced nutrient metabolism and gut barrier function. Moreover, MOS supplementation significantly increased alpha diversity of the gut microbiota, altered community composition, and promoted the abundance of beneficial genera, including Clostridium and Bacteroides. Collectively, these results demonstrate that MOS supplementation improves metabolic health, modulates immune and antioxidant responses, and fosters a beneficial gut microbial ecosystem in lactating donkeys, suggesting its potential as an effective prebiotic in equine nutrition.

Yeast hydrolysate (YH) is a yeast-derived functional feed ingredient containing bioactive peptides, amino acids, nucleotides, β-glucans, and mannan oligosaccharides, which may exert prebiotic-like effects by regulating nutrient metabolism, host health, and intestinal microbial homeostasis. However, its effects on lactating Dezhou jennies remain largely unclear. This study investigated the effects of dietary YH supplementation on body weight change, serum biochemical parameters, serum metabolomic profiles, and fecal microbiota composition in lactating Dezhou jennies. Sixteen healthy lactating Dezhou jennies were randomly assigned to a control group fed a basal diet (MCON, n = 8) or a YH supplementation group fed the basal diet supplemented with YH (MYE, n = 8) for 60 days. Compared with the MCON group, the MYE group showed numerically higher final body weight and body weight change. Serum biochemical analysis showed that YH supplementation significantly decreased alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities and increased triglyceride (TG) concentrations, while all measured biochemical parameters remained within physiological reference ranges. Serum metabolomic profiling identified 193 differential metabolites between the two groups, including 55 upregulated and 138 downregulated metabolites in the MYE group. These metabolites were mainly associated with amino acid metabolism, lipid metabolism, bile acid metabolism, steroid hormone biosynthesis, mineral absorption, ABC transporters, and protein digestion and absorption, indicating that YH supplementation reshaped nutrient-related metabolic pathways in lactating Dezhou jennies. Fecal microbiota analysis showed no significant changes in α-diversity or overall community structure; however, the MYE group displayed numerically higher microbial richness indices, more unique ASVs and genera, a lower relative abundance of Bacteroidota, and a higher relative abundance of Bacillota. LEfSe analysis further revealed enrichment of specific bacterial taxa in the MYE group, including Christensenellaceae_R-7_group, Anaerovorax, and UCG-related taxa. Collectively, these preliminary findings suggest that dietary YH supplementation may alter selected serum biochemical indices and circulating metabolites and may selectively affect the relative abundance of certain fecal bacterial taxa in lactating Dezhou jennies. However, given the limited sample size, these results should be interpreted cautiously, and larger-scale studies are needed to confirm their reproducibility and practical significance.