34. Dose-response Relationship of a Blended Tannin Extract on Ruminal Fermentation Dynamics, Methane Production, and Diet Digestibility Using the In Vitro Gas Production Technique.

Abstract Dietary tannins can modulate rumen fermentation and reduce methane (CH4) production, yet dose-response data for blends containing both condensed tannins (CT) and hydrolyzable tannins (HT) remain limited. This study evaluated the effects of a blended tannin extract (TE) containing CT and HT (SilvaFeed ByPro; SILVATEAM, San Michele Mondovi, Italy) on ruminal fermentation dynamics, CH4 production, and diet digestibility using the in vitro gas production technique with ruminal fluid inoculum from treatment-adapted steers. Eight British crossbred steers (215±18 kg) were used in a 4 × 8 Latin rectangle design, with two steers per treatment per period. In each period, steers were randomly assigned to treatments and rotated across periods, with each steer receiving each treatment once during the trial. Treatments were TE at 0, 0.15, 0.3, or 0.45% of dietary dry matter (DM; TE0, TE0.15, TE0.3, TE0.45). Each period lasted 23 d, during which steers received their assigned TE treatment mixed individually into their total mixed ration (TMR). Rumen fluid inoculum was collected from each donor steer and placed in individual bottles containing a subsample of the TMR for 48-h incubations. Each incubation (run) evaluated two TE treatments at a time, using one donor steer for each treatment per run and ten randomly assigned bottles per donor. Gas production was recorded over time to estimate fermentation kinetic parameters (e.g., total gas, fractional rates of gas production, and lag time). Post-fermentation, headspace gas was analyzed for CH4 via gas chromatography. Fermentation kinetics were characterized using both an exponential model and a log-2 pool model separating non-fiber (NFC) and fiber carbohydrate (FC) pools. Dose-response relationships were evaluated using mixed-effects polynomial regression, with period, donor animal, and run-within-period as random effects. Based on the exponential model, a significant cubic relationship was observed between TE inclusion rate and total gas production, fractional rate of gas production, and fermentation lag time (P ≤ 0.01). Furthermore, the log-2 pool model revealed significant cubic responses for the fractional rate of the NFC pool, the lag time, cumulative gas production, and the fractional rate of the FC pool (P ≤ 0.03), as well as the exponential decay rate of digestion (P = 0.01). Total CH4 production and CH4 per gram of fermentable organic matter displayed a cubic pattern (P < 0.01), with the lowest CH4 observed for TE0.45. There was a significant cubic effect for computed total digestible nutrients (TDN) and metabolizable energy (ME) values (P = 0.02); however, TE inclusion rate did not influence ivNDFD (in vitro neutral detergent fiber digestibility; P ≥ 0.63). Results suggest that a 0.45% dietary DM inclusion of the TE optimizes in vitro CH4 mitigation. Further in vivo trials are warranted to validate this optimal inclusion level.