Reducing enteric methane emission in dairy goats: impact of dietary inclusions of quebracho tannin extract on ruminal microbiota

Introduction: Condensed tannins (CT) influence ruminal microbiota, feed
digestibility, and methane emissions, yet their effects in goats are poorly
understood.
Methods: This study evaluated the impact of dietary quebracho CT extract at
0%, 2%, 4%, or 6% of dry matter on the composition of the dairy goat ruminal
microbiota with a two-times repeated 4 × 4 Latin square design. Bacterial,
archaeal, fungal, and protozoan communities were analyzed at the end of each
feeding period for relative abundance changes, and their relationship to methane
production, nutrient digestibility and feed efficiency were also assessed.
Results: Increasing CT levels reduced alpha- and beta-diversity, with the
6% CT diet showing the most pronounced decline. CT inclusion induced
phylum-level shifts in fiber-degrading microbes, including inversion of the
Firmicutes to Bacteroidota ratio. Prevotellaceae and Succiniclasticum, tolerant
to CT, increased significantly (P < 0.05), in line with higher propionate and
lower methane production. The proteolytic bacteria Anaerolineaceae and
Synergistaceae decreased (P < 0.05), consistently with the reduced isobutyrate
and isovalerate ruminal concentration and with the reduced urinary nitrogen
excretion. Methanobrevibacter, a key methane producer, was reduced by dietary
CT (P < 0.05). The overall fungal biodiversity was also significantly changed
(P < 0.05); the fiber-degrading Liebetanzomyces decreased, while the tannin-
degrading Aspergillus increased (P < 0.05). Concerning protozoa, Diplodinium
was reduced (P < 0.05) and Polyplastron and Isotrichia were increased (P < 0.05)
by dietary CT.
Discussion: These and other microbial abundance changes correlated with
reduced methane emission, altered fiber and protein digestibility, and modified
volatile fatty acid (VFA) profiles. This study shows that decreased nutrient
degradability in the rumen due to higher dietary CT alters the goat rumen
microbiota and clarifies microbial taxa changes in relation to the zootechnical
outcomes, including reduced methane production.