Correlation between gastrointestinal morphological changes, enteric microbiota, and changes in live weight in dairy calves.

This study aimed to quantify the association between fecal microbiota biomarkers, gastrointestinal tract morphology, and ADG of dairy calves from birth until weaning in response to feeding a direct-fed microbial (DFM) supplement as part of their milk diet. We randomly assigned 44 newborn Holstein-Friesian calves to treatment (TRT) and control (CON) groups. The TRT group calves received a once-daily dose of - and -based DFM liquid formulation. Four genera, 7, , and , were enriched and identified as biomarkers of low ADG. A total of 14 bacterial taxa were associated with measured gastrointestinal histopathology variables in TRT and CON groups. Although this study lists several bacterial taxa that have known roles in fermentation and nutrient metabolism vital for rumen function, their specific contributions to gastrointestinal development and weight gain remain to be fully understood. Our findings support a strategic approach to probiotic use in heifers to boost health and productivity.