Can Marandu Grass ( Urochloa brizantha ) Extract Modulate Methanogenesis and Rumen Microbiota?

Urochloa spp. are the most important grasses for ruminants in Brazil and contain secondary metabolites, mainly saponins. Urochloa brizantha extracts (ethanolic EE and hydroalcoholic HE with 3.62 and 5.38 mg protodioscin mL −1 , respectively) were developed to verify their potential as additives for ruminant nutrition. The in vitro gas production technique was used to evaluate ten treatments in a completely randomized factorial arrangement (2 × 4 + 2), where the main effects were two extracts (EE and HE); four levels (50, 100, 150, and 200 mL of the extract kg −1 of DM), plus two controls (one positive with 25 ppm of monensin and another with no additives). The extracts EXT (EE and HE) produced a higher proportion of acetate (C2) and lower propionate (C3) than CTL, reflected in a 31% higher C2:C3 ratio. However, there was no significant difference ( p > 0.05) between the treatments for methane production parameters. Archaea and Ruminococcus’ relative gene expressions were higher in EE than in HE; however, the protozoa opposite occurred, HE was higher than EE. Fibrobacter succinogenes were 33% lower in EXT than in CTL. The addition of these extracts in a sheep diet increased the production of SCFA and decreased Fibrobacter succinogenes without altering the methane and archaeal population.