35. Effect of Donor Adaptation to Tannin Extract on Methane Production in an In Vitro Rumen Fermentation System.

Abstract Enteric methane (CH4) production from ruminant livestock contributes to greenhouse gas emissions and represents an energy loss during ruminal fermentation. Tannins have been investigated as a dietary strategy to reduce CH4 production; however, the response of rumen fermentation to tannin supplementation may depend on prior exposure of animals to tannin-containing diets. Therefore, the objective of this study was to evaluate whether adaptation of donor animals to a tannin-containing diet affects CH4 production measured using an in vitro gas production (IVGP) system. A 2 × 2 factorial design was used to evaluate the effects of tannin extract (TE) adaptation of donor animals (TEA; adapted = TEA-Y or non-adapted = TEA-N) and in vitro tannin inclusion (ivTE; absent = ivTE-N or added during incubation = ivTE-Y). Eight ruminally cannulated crossbred Angus steers (380 ± 30 kg BW) were used as rumen fluid donors. Four animals were adapted to a TE–containing diet (60:40 roughage:concentrate) with 0.2% of dietary DM tannin inclusion for 21 d prior to the study, while four animals received the same diet without TE during the same period. Rumen fluid was pooled within dietary group and used as inoculum for IVGP incubations, with TE added to randomly selected bottles also at 0.2% DM. Methane production (mg) and CH4 yield relative to fermentable organic matter (mg/g FOM) were measured. Data were analyzed using a mixed model including TEA, ivTE, and their interaction as fixed effects and run as a random effect. Model assumptions were evaluated using residual diagnostics, and influential observations were identified using studentized residuals and Cook’s distance. The interaction between donor adaptation (TEA) and in vitro tannin inclusion (ivTE) was not significant for total CH4 production (P = 0.758) or CH4 yield (P = 0.402), indicating similar responses to TE addition for TEA-Y and TEA-N inoculum sources. Donor adaptation (TEA-Y vs. TEA-N) did not affect total CH4 production (P = 0.164). Similarly, in vitro tannin inclusion (ivTE-Y vs. ivTE-N) did not affect total CH4 production (P = 0.094). However, when CH4 was expressed relative to fermentable organic matter, bottles receiving tannin inclusion (ivTE-Y) reduced CH4 production when compared to bottles without tannin (ivTE-N) (P = 0.017). Overall, these results indicate that prior dietary adaptation of donor animals to the tannin extract evaluated did not alter the microbial response to tannin supplementation under the controlled conditions of the IVGP system. These findings suggest that donor adaptation may not be necessary when evaluating TE-based additives using IVGP techniques and that direct tannin inclusion during incubation is the primary factor influencing CH4 yield.