Milk Production and Enteric Methane Emissions in Dairy Cows Grazing Annual Ryegrass Alone or Intercropped with Forage...

This study evaluated the effects of reduced nitrogen fertilization and the intercropping of annual ryegrass (Lolium multiflorum Lam.) with forage legumes-common vetch (Vicia sativa L.) and red clover (Trifolium pratense L.)-on milk production and enteric methane emissions in grazing dairy cows. Twelve Holstein × Jersey cows were assigned to a crossover design involving two treatments: ryegrass monoculture (RG) or ryegrass-legume mixture (RG + Leg). Methane emissions were measured using GreenFeed systems; grazing behavior, milk yield and composition, and organic matter digestibility were also assessed. Legume inclusion contributed ~9% of the pre-grazing biomass, and cows grazing RG + Leg pastures had lower herbage mass (-214 kg DM/ha) and lower herbage allowance (-6 kg DM/cow/day) than cows on monoculture ryegrass. Energy-corrected milk (ECM), methane emissions (g/day and g/kg ECM), and grazing behavior were not significantly affected by treatment. These results suggest that, under subtropical grazing conditions, reducing nitrogen fertilization combined with the modest inclusion of vetch and red clover does not mitigate enteric methane emissions nor enhance animal performance. Enhanced strategies to increase legume proportion in mixed swards are needed to unlock their potential for sustainable intensification of pasture-based dairy systems.