Effects of the Flavonoid Rutin and Monensin on In Vitro Rumen Fermentation of Total Mixed Rations Differing in Forage-to-Concentrate Ratio

Background: Plant flavonoids are candidate alternatives to ionophores for modulating rumen fermentation, yet the intact glycoside rutin (quercetin-3-O-rutinoside) has received little attention. The objective of this study was to determine whether rutin changes the in vitro ruminal fermentation of total mixed rations (TMR) differing in forage-to-concentrate ratio; monensin was included at a single dose as a reference additive rather than a direct comparator. Methods: In a 2 × 4 factorial batch-culture experiment, a roughage-based (60:40) and a concentrate-based (40:60) TMR were incubated for 24 h without additive (control) or with rutin at 2.5% or 5% of substrate dry matter or monensin at 30 ppm. Results: Rutin did not change the gas production kinetics, ruminal pH, the volatile fatty acid (VFA) profile, or the stoichiometrically estimated methane and carbon dioxide at either dose (p > 0.05), and no dose response was found. Substrate type likewise left the VFA profile and the estimated gases unchanged (p > 0.05). Ammonia nitrogen (NH3-N) responded to the additive group (p = 0.027) and to the substrate × additive interaction (p = 0.022), but Tukey comparisons separated no individual means, so this response is preliminary. Conclusions: Neither rutin nor monensin markedly altered fermentation of these silage-, alfalfa- and cereal-based rations in the 24 h batch system; the substrate-dependent NH3-N signal warrants confirmation, and direct methane measurement is required before any anti-methanogenic potential can be claimed.