Folic acid supplementation enhances growth and modulates faecal microbiota and metabolite profiles in pre-ruminal Holstein calves

This study investigated the effects of folic acid supplementation on growth performance, faecal microbiota composition, and faecal metabolomic profiles in pre-ruminal Holstein calves. Twenty newborn female calves were randomly assigned to either a control group (n = 10) or a folic acid–supplemented group (2.5 mg/day; administered orally; n = 10) from birth to 56 days of age. Body weight, feed intake, and serum biochemical parameters were recorded periodically. Faecal microbiota was analysed by 16S rRNA gene sequencing and quantitative real-time PCR, and faecal metabolomic profiles were assessed by gas chromatography–mass spectrometry (GC-MS). Folic acid supplementation significantly increased weight gain, accompanied by elevated serum folic acid and insulin-like growth factor 1 (IGF-1) concentrations. Red blood cell counts increased in the supplemented group, whereas mean corpuscular haemoglobin decreased. Faecal microbiota analysis at 14 days of age revealed a significant enrichment of Blautia in the folic acid group. Although no faecal metabolites showed significant group differences after FDR correction, Pearson correlation analysis revealed that Blautia abundance was broadly and positively correlated with branched-chain amino acids and their keto acid intermediates, aromatic amino acids and their microbial fermentation products, and other amino acid-related metabolites. These findings indicate that folic acid supplementation during the pre-ruminal period promoted calf growth and modulated the faecal microbiota, with exploratory correlation analyses suggesting potential associations between Blautia enrichment and faecal amino acid profiles that warrant further investigation.