Methane and carbon dioxide emissions from lactating dairy cows grazing mature ryegrass/white clover or a diverse pasture comprising ryegrass, legumes and herbs

There is a growing interest in forage mixtures (Diverse pasture; e.g. containing grasses, legumes and herbs), especially those with a greater tolerance of dry conditions and a decreased nitrogen (N) content (reducing N losses), compared with ryegrass (Lolium perenne L and Lolium multiflorum L)/white clover (Trifolium repens L) pastures (RyeWC), which dominate New Zealand pastoral systems for dairy production. However, the effect of alternative forages on enteric methane (CH₄) emissions is not known. The objective of the present trial was to compare CH₄ emissions and milk production from dairy cows grazing either mature RyeWC or mature Diverse pasture (both approximately with pasture mass of 5600 kg DM/ha). The Diverse mixture comprised ryegrass, white clover, lucerne (Medicago sativa L), chicory (Cichorium intybus L) and plantain (Plantago lanceolata L). Milk production, measured from cows commencing at ∼162 days of lactation, was less when cows grazed RyeWC than Diverse pastures (15.4 vs 16.7 kg/day; P < 0.001), whereas CH₄ production (g/day) was similar for the respective treatments (411 g/day; P = 0.16). Milk composition was not affected by diet and CH₄ intensity was similar for both diets (22 g/kg fat-and protein-corrected milk; P = 0.31). Methane yield [g/kg predicted dry matter intake (DMI)] averaged 22.6 and 24.9 for cows grazing RyeWC and Diverse pastures, respectively (P = 0.006). In conclusion, although the CH₄ yield was greater when Diverse pasture was grazed, relative to RyeWC, there were no differences in emissions intensity or total CH₄ emissions