Dose–response effects of a mixed condensed and hydrolyzable tannin extract on methane production and diet digestibility using the in vitro gas production technique

Several studies have evaluated the impact of isolated condensed or hydrolyzable tannin extract (TE) supplementation for beef cattle on methane (CH4) mitigation and metabolic functions, but fewer have evaluated their combination. Our objective was to investigate changes in in vitro fermentation dynamics, CH4 production, neutral detergent fiber digestibility (ivNDFD), and ruminal volatile fatty acid (VFA) concentrations in response to the inclusion rate of a TE blend (Silvafeed ByPro; SILVATEAM). Inclusion of TE at 0.0%, 0.3%, 0.6%, and 0.9% DM (TE0.0, TE0.3, TE0.6, and TE0.9), within a total mixed ration, was evaluated using four in vitro incubations. Fresh rumen inoculum from two ruminally cannulated donor steers was used for each incubation. Mixed-effects polynomial regression models, with incubations as the random effect, were used for dose-response analysis. The inclusion rate did not affect total gas production (P ≥ 0.67) determined from an exponential model. The fractional rate of exponential gas production decreased linearly (P < 0.01) with increasing inclusion. The lag time for initiating gas production displayed quadratic (P < 0.01) and cubic (P = 0.01) patterns. Based on the log 2-pool model, cumulative gas production from both carbohydrate pools was influenced by inclusion rate in a cubic (P ≤ 0.01) fashion, but in opposite directions. Cumulative gas production for the nonfiber carbohydrate pool peaked at 0.05% DM inclusion and reached a minimum at TE0.9, while that of the fiber carbohydrate (FC) pool was minimized at 0.21% DM and peaked at TE0.9. There was a quadratic (P = 0.04) effect for the lag time to begin fermentation of the FC pool. Total CH4 production displayed a cubic (P = 0.04) pattern in response to TE inclusion, with minimum production at 0.18% of DM. Production of CH4 per g of fermentable organic matter tended (P = 0.06) to follow the same cubic pattern. There was no influence of inclusion rate on ivNDFD (P ≥ 0.68) or computed energy values (P ≥ 0.67). Ruminal pH and total VFA concentration were not affected by treatment (P ≥ 0.11), but propionate linearly decreased (P = 0.02) and the acetate: propionate ratio linearly increased (P < 0.01) with increasing TE inclusion. Our results suggest that inclusion of TE at 0.18% of DM has the greatest potential for in vitro CH4 mitigation. Further research is warranted to determine the dose-response relationships between the supplementation rate of this TE and in vivo CH4 production and ruminal parameters.