Effects of multispecies and monoculture forages on nutrient digestibility and fermentation responses using an in vitro rumen simulation technique (RUSITEC)

Enteric methane (CH₄) emissions are a major contributor to global greenhouse gas emissions. A number of different CH₄ mitigation strategies have been proposed, and the inclusion of alternative forages into grazing systems could be a practical and feasible option. Multispecies swards comprise a mixture of forage species and can increase grassland productivity, reduce nitrogen fertiliser requirements, and reduce fertiliser-associated nitrous oxide emissions. This study investigated the potential benefit of multispecies swards in reducing ruminal CH₄ production. Using the in vitro rumen simulation technique, we compared the effects of different forages (perennial ryegrass, timothy, red clover, white clover, chicory, ribwort plantain and their equi-proportional mixture) on CH₄ and gas production, ruminal fermentation parameters and nutrient digestibility. We also compared these responses to perennial ryegrass produced with a higher nitrogen application rate (300 N). The experiment was conducted over 21 d, with the initial 14 d allowed for dietary adaptation. Over the subsequent 7 d, there were significant effects of forage type on CH₄ production, ruminal fermentation and digestibility. Ribwort plantain, chicory and white clover showed lower CH₄ production; with chicory producing 73% and 57% less CH₄ (mmol d⁻¹) compared to 300 N perennial ryegrass and 150 N perennial ryegrass incubation, respectively. Chicory had 72% lower CH₄ produced per gram of organic matter digested (mmol g⁻¹) than that of 300 N perennial ryegrass. Chicory and 300 N perennial ryegrass had greater (P < 0.01) organic matter and nutrient digestibility (DM, CP, NDF, and ADF) than other forages. Greater ammonia nitrogen concentration was observed in chicory and both clover species, compared to the other forage species (P < 0.01). In general, the response of the six-species mixture was not significantly different to the average response of the six component monocultures. Thus, from these data, the performance of multispecies swards for these responses (in general) was predictable from the performance of the component monocultures. These results showed that different grassland forages, especially chicory and white clover, have the potential to reduce ruminal CH₄ emissions and could be a promising anti-methanogenic alternative to chemical CH₄ inhibitors and feed additives. More generally, the relatively wide variation in CH₄ abatement potential across a small sample of plant species suggests the merit of wider screening to identify grassland species with high CH₄ abatement potential in vitro.