Effects of dietary supplementing tannic acid in the ration of beef cattle on rumen fermentation, methane emission, microbial flora and nutrient digestibility.

Four adult Simmental male cattle (376 ± 9.0 kg initial BW), fitted with permanent rumen cannulas, were used in a 4 × 4 Latin square design to investigate the effects of dietary supplementing tannic acid (TA) on rumen fermentation, methane (CH4 ) production, rumen microbes, nutrient digestibility and plasma biochemical parameters. Four levels of TA, that is 0, 6.5, 13.0 or 26.0 g/kg dry matter (DM), were added to the basal ration (composed of corn silage and concentrate mixture) as experimental treatments respectively. Each experimental period consisted of a 12-day adaptation phase followed by a 3-day sampling phase. The results showed that supplementing TA at 26.0 g/kg DM decreased the relative abundance of protozoa, methanogens and Ruminococcus albus to the total ruminal bacterial 16S rDNA in beef cattle (p < 0.05). The results also showed that supplementing TA at 6.5, 13.0 or 26.0 g/kg DM decreased (p < 0.01) the CH4 production (l/kg DM intake) by 11.1%, 14.7% and 33.6% respectively. Supplementing TA at 13.0 or 26.0 g/kg DM decreased the ratio of acetate to propionate and ammonia nitrogen (NH3 -N) (p < 0.05) and tended to decrease the total volatile fatty acid (VFA) concentration of rumen fluid (p = 0.07). Supplementing TA at 26.0 g/kg DM decreased DM and organic matter (OM) digestibility (p < 0.05), supplementing TA at 6.5, 13.0 or 26.0 g/kg DM decreased (p < 0.01) crude protein (CP) digestibility by 5.0%, 8.6% and 15.7%, respectively, and supplementing TA at 6.5, 13.0 or 26.0 g/kg DM increased (p < 0.05) the plasma total antioxidant capability. It was concluded that supplementing TA in the ration of beef cattle decreased the CH4 production and digestibility of CP of beef cattle. Supplementing TA could be an effective option to mitigate CH4 emission form cattle, further research is necessary to study the effects of TA on the performance of cattle.