Tannins in reducing diarrhoea incidence and methane emissions from a long-term perspective in dairy calves.

Pre-weaning diarrhoea remains a major challenge in dairy farming, contributing to substantial economic losses and negatively impacting the future health and productivity of dairy cows. Growing concerns over antimicrobial resistance and the limited effectiveness of antibiotics led to investigating alternative strategies, particularly nutritional approaches that enhance calf health and resilience. Among these, tannins and tannin-rich plant extracts have gained interest for their properties. Hydrolysable tannins tend to exert stronger antimicrobial and cytoprotective activities, whereas condensed tannins are more effective in modulating rumen fermentation and reducing methane formation. In neonatal calves, tannins show promise as natural feed additives to support gut health and immune development. Studies suggest that tannins can reduce both the incidence and duration of pre-weaning diarrhoea by modulating gut microbiota and protecting intestinal epithelial cells. These benefits may also extend beyond the pre-weaning phase, contributing to improved gut function and potentially lowering enteric methane emissions through their influence on rumen microbial colonization. This review examines the effects of tannins from various sources on calf health, production efficiency, and long-term environmental impact. It also emphasizes the need for further research to determine optimal dosage levels in neonatal ruminants, given the variability among tannin types and sources. In conclusion, the targeted use of tannins in the diets of pre-weaned dairy calves offers a promising strategy to improve gut health, reduce antibiotic reliance, and enhance overall calf resilience. However, their practical application must be guided by robust evidence and safety thresholds to ensure effectiveness and animal welfare.