Effects of Fecal Microbiota Donor on the Intestinal Microbiome, Health, and Growth of Preweaning Calves

<title>Abstract</title> <p>Environmental spraying of microbiota is a novel low-stress strategy for manipulating early microbial colonization. This study aimed to compare the effects of spraying Fecal Microbiota (FM) from calves and lactating cows on the growth, health, and intestinal microbiota of preweaning calves A total of 60 newborn calves were randomly divided into three groups: control group (CON), weaned calf fecal microbiota group (WCFG): sprayed with microbiota from weaned cow feces, and lactating cow fecal microbiota group (LCFG): sprayed with microbiota from lactating cow feces. Growth performance, serum biochemical parameters, immune indicators, and intestinal microbial composition were monitored. Compared with the CON and WCFG, the LCFG exhibited significant impairment in growth performance, including a marked decrease in body weight (BW) on day 60, significantly reduced average daily gain (ADG) during days 15–30 and 45–60, and a significantly higher diarrhea rate. Serum analysis revealed systemic metabolic and immune disorders in the LCFG, characterized by decreased blood glucose (GLU), increased alanine aminotransferase (ALT), and altered inflammatory cytokine profiles. Intestinal microbiota analysis indicated that the LCFG developed a unique and potentially dysregulated microbial structure, featuring a reduction in beneficial bacterial genera and enrichment of other genera. Spraying FM from lactating cows induces a series of negative effects, including intestinal dysbiosis, systemic physiological disorders, and ultimately impaired growth in preweaning calves. These findings highlight that environmental fecal microbiota can affect intestinal microbial colonization in preweaning calves.</p>