Potential roles of colostrum microbiota in shaping calf gut microbiota and colostrum metabolites

Colostrum provides vital nutrients and antibodies that are crucial for calf health and survival. It also contains microbes that may be vertically transmitted to calves and influence early gut microbiota development. These microbes in colostrum may also biologically function to produce unique metabolites that affect colostrum quality and calf growth. However, these colostrum components remain largely unexplored. The aim of this study was to identify colostrum-derived microbes capable of colonizing and persisting in the calf gut and to characterize colostrum metabolomics in relation to the colostrum microbiota. Colostrum samples were collected from 25 Holstein heifers, and fecal samples were collected from their individually housed Holstein-Angus crossbred offspring on d 4, 7, 14, and 30 after birth. Colostrum and fecal microbiota were analyzed using full-length 16S rRNA gene amplicon sequencing, while the untargeted metabolomics was performed using ultra-performance liquid chromatography-mass spectrometry. We identified 20% prevalent colostrum bacteria (15 species) were consistently detected in calf fecal samples across all time points, indicating their potential to colonize and persist in the early gut, although the relative abundance of these species in calf feces gradually reduced from d 4 to d 30. Colostrum samples were classified into 3 distinct clusters based on the dominant species: Streptococcus thermophilus, Lactococcus lactis, and Comamonas testosteroni . Three colostrum samples from each cluster were selected as a focal group for the untargeted metabolomics analysis. We identified a total of 405 metabolites present in the colostrum samples. No significant differences in metabolomic profiles were observed among the 3 microbial clusters, indicating that colostrum microbiota were not the main drivers of metabolomic dynamics. However, 54 strong positive correlations were detected between bacterial species and metabolites, particularly between colostrum-calf feces shared species and microbial-derived metabolites. For example, Butyricicoccus pullicecorum was positively correlated with 4-methylphenol and 5-hydroxyindole, while 4-methylphenol was also associated with Bacteroides fragilis , the most abundant bacterial species in calf feces on d 4. In addition, Streptococcus uberis , a pathogen associated with mastitis, exhibited the greatest number of strong negative correlations with metabolites. In conclusion, this study identified specific colostrum bacterial species with the potential to transmit and persist in the calf gut microbiota and to contribute to microbial metabolite production. Further research is warranted to evaluate the roles of these persistent microbes and their metabolites in shaping colostrum quality, calf growth, and health outcomes.