Serum physiology, fecal microbiota, and metabolome signatures associated with perinatal stage transitions in Mongolian mares.

INTRODUCTION: Lactation is a critical reproductive trait that influences offspring survival and livestock productivity in equine production. Characterizing physiological transitions during the perinatal period can improve our understanding of how mares adapt to late gestation, parturition, and early lactation. However, in horses-a typical monogastric herbivore with unique digestive characteristics-the associations between gut microbiota and perinatal physiological adaptation, as well as related stage-associated microbial and metabolic features, remain largely uncharacterized. METHODS: In this study, parallel profiling of serum physiology, fecal microbiota, and fecal metabolome was performed to identify candidate stage-associated microbial and metabolic features across three perinatal stages (pre-foaling, PF; post-foaling, PoF; early lactation, EL) in 19 multiparous Mongolian mares selected from a local breeding herd with records of normal foaling and healthy weaning. We further systematically determined serum biochemical indicators, reproductive hormones and immune parameters to interpret host physiological adaptive characteristics linked to lactogenesis. RESULTS: Obvious stage-specific physiological patterns were observed: triglycerides, urea and mineral elements were present at higher serum concentrations during the pre-foaling period, which may support fetal gestation; serum glucose was higher after parturition, which may meet the energy demands of delivery and early lactation; serum IgA concentration was higher in early lactation, which may be consistent with enhanced mucosal immune activation. Of note, serum IgA does not directly reflect colostral IgA concentrations or foal passive immunity. Alpha diversity of fecal microbiota was lower during the post-foaling stage, and each perinatal stage was associated with distinct fecal microbial community structures. Microbial taxa potentially associated with carbohydrate fermentation were more abundant in the pre-foaling period; the post-foaling stage was associated with an increased relative abundance of Akkermansia, which is consistent with a possible role in intestinal barrier maintenance, along with increased PICRUSt2-predicted abundance of galactose metabolism pathways; microbial taxa potentially related to lipid metabolism and bile secretion features were predominant in early lactation. DISCUSSION: This study systematically characterized stage-specific remodeling patterns of fecal microbiota and fecal metabolome during the perinatal transition in Mongolian mares. The identified fecal microbial taxa and metabolites are described as candidate stage-associated discriminatory features rather than validated biomarkers.