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

Abstract

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.