Fecal microbiota succession in dairy calves is driven by age and modestly influenced by colostrum source

Colostrum is crucial for the survival and health of neonatal calves, providing passive immunity and influencing early gut microbial colonization. This study evaluated the impact of three colostrum sources: fresh maternal colostrum (FMC), frozen maternal colostrum (FC), and colostrum replacer (CR) on the development of the fecal microbiota in Holstein calves. Fifteen newborn calves were randomly assigned to one of three treatments (n = 5 per group). Fecal samples were collected at birth (meconium), daily during the first seven days of life, and at weeks 2, 4, 8 (weaning), and 10 (post-weaning). Microbial composition was assessed using 16 S rRNA gene sequencing. Alpha diversity increased over time (P < 0.001), with no significant differences observed among treatments. Microbiota succession followed a consistent trajectory across all groups, characterized by an early dominance of Escherichia/Shigella, which gradually transitioned to increased relative abundances of Lactobacillus, Bacteroides, and Faecalibacterium over time. Notably, calves fed FMC showed a significantly higher fecal relative abundance of Lactobacillus during the first three days of life (excluding day 0, meconium) compared to those receiving FC (P = 0.046) or CR (P = 0.44), although the overall bacterial community structure was primarily influenced by calf age. These findings suggest that while colostrum source does not impact overall microbial diversity, it may modulate early colonization by beneficial bacteria. Providing fresh maternal colostrum may promote more favorable microbiota programming during the neonatal period.