Unlocking the potential of willow condensed tannins: effects on rumen fermentation, microbiome, and metabolome for sustainable ruminant nutrition.

Background: Sustainable livestock production is essential for meeting the growing global protein demand while minimising environmental impacts. Exploring alternative forages that enhance nutrient utilisation and reduce reliance on imported feeds is a potential strategy. Condensed tannins (CTs) can bind to proteins in the rumen, protecting them from ruminal degradation resulting in decreased ammoniacal N and enhanced nitrogen uptake in the hindgut. This pioneering research is the first to explore the potential of willow (Salix) as an alternative feed for ruminant nutrition. The study involved feeding ewe hoggets a control grass silage (SIL) or a SIL mix containing a 20% dry matter (DM) dietary inclusion of leaves from two willow varieties to investigate the impact the willow CTs have on rumen fermentation, microbial populations, and metabolomic profiles. Willow treatments: Beagle (BG) and Terra Nova (TN) had an overall CT inclusion (CTI) of 1.1 and 0.1% DM with the control diet containing no CTs in a three-treatment x three-period Latin square design.

Results: Although total dry matter and fibre intake were higher in BG and TN, there was no significant difference in ruminal CH₄ production between the treatments. However, fermentation was affected, with BG and TN showing lower acetate production and reduced total volatile fatty acid production compared to SIL. CTs may have impaired fibre digestion, as SIL had higher Fibrobacter abundance than BG. Heatmap visualisation indicated higher carbohydrate metabolite concentrations in SIL, with reduced metabolism observed in TN and BG. Ruminal ammonia did not differ significantly among treatments, despite higher nitrogen intake in BG and TN treatments. Proteolytic bacteria levels were similar across treatments, but TN and BG had higher ruminal metabolites associated with protein metabolism upon visualisation through heatmap analysis. TN showed higher abundance of Prevotella and Fibrobacter than BG, which had 10 times higher CT content and a greater prodelphinidin proportion.

Conclusion: Feeding CT-containing willow enhanced feed intake, altered rumen microbiome composition and suggested visual changes in the analysis of protein metabolism, offering potential benefits for animal performance. While a reduction in CH₄ was not observed, this study highlights the potential of willow to alter ruminant nutrition while supporting sustainable agricultural practices.